No. Wait, Maybe

Can an even number, divided by another even number, times another even number ever equal an odd number?

If "yes," then find three numbers that work.
If "no," then why not?

Note that the three even numbers can be different numbers.

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55 solutions

Discussions for this problem are now closed

Zandra Vinegar Staff
Sep 30, 2015

Woah! This problem definitely tricked me when I first saw it! Then I wrote things out algebraically, and it was still tricky to figure out exactly what's going on. It's a wonderful question!


SOLUTION:

An even number is any number of the form 2 x 2x where x x is any whole number (integer). So the problem asks "Is it possible for 2 x 2 y × 2 z \frac{2x}{2y} \times 2z to equal an odd number?"

Now, let's use algebra:
2 x 2 y × 2 z = x y × 2 z = 2 x z y \frac{2x}{2y} \times 2z = \frac{x}{y} \times 2z\ = \frac{2xz}{y}

This makes it much clearer what needs to happen: y y must have a factor of 2 , so that 2 can cancel out the 2 in the numerator of 2 x z y \frac{2xz}{y} .

As an example x=3, y=6, z=5 \fbox{x=3, y=6, z=5} will work. Our even numbers are then 2 x = 6 2x = 6 , 2 y = 12 2y = 12 , and 2 z = 10 2z = 10 .

6 12 × 10 = 5 \frac{6}{12} \times 10 = 5 and 5 is odd, so we're done. However...


GENERALIZATION:

To generalize, consider: 2 x z y \frac{2xz}{y}\ more closely. What does it take in order for the tuple of even numbers { 2 x , 2 y , 2 z 2x, 2y, 2z } to have the property that 2 x z y = 2 x 2 y × 2 z = \frac{2xz}{y} = \frac{2x}{2y} \times 2z = some odd integer?

1) Observe that in order for 2 x z y \frac{2xz}{y} to be an integer, y y must be a factor of 2 x z 2xz .
2) In order for 2 x z y \frac{2xz}{y} to be odd, y y must be a factor that is itself divisible by the highest power of 2 that 2 x z 2xz is divisible by.

The easiest way to see the necessity of both of these facts is to consider the prime factorization of all of the numbers ( x , y , x, y, and z z ) involved, and to know that in order for the resulting product to be odd, all of the 2s must cancel.


FOLLOW-UP CHALLENGE:

If x = 12 x=12 and z = 30 z=30 . What value(s) of y y will make 2 x 2 y × 2 z \frac{2x}{2y} \times 2z odd?

In other words, can you make 24 2 y × 60 \frac{24}{2y} \times 60 odd?

First, we factor:
x = 12 = 2 2 × 3 x=12=2^2 \times 3
z = 30 = 2 × 3 × 5 z=30=2 \times 3\times 5

As per the argument above, y y must be a multiple of 2 2 + 1 + 1 = 2 4 = 16 2^{2+1+1} = 2^4 = 16 that is also a factor of 2 4 × 3 2 × 5 = 720 2^4 \times 3^2 \times 5\ = 720 . So, any of 16, 48, 80, 144, or 720 \fbox{16, 48, 80, 144, or 720} will work.

Let's test y = 48 y=48 .

2 x 2 y × 2 z = 24 96 × 60 = 15 \frac{2x}{2y} \times 2z = \frac{24}{96} \times 60\ = 15

Boom! Solved and generalized!

It should be more clear that the "even/even" number is allowed to be a fraction, because this is the only way possible. I missed it because of it, I thought every factor there should be integer

Felipe Magnus - 5 years, 4 months ago

Ahhh, i missed the word ever

Ashish Menon - 5 years, 3 months ago

Excellent, beautiful and a detailed explanation.

Mehdia Nadeem - 5 years, 8 months ago

Good explanataion. It is crystal clear.

Chandan Ghughtyal - 5 years, 6 months ago

let three even numbers be 2,4 and 6 4/2 x 6 = 12........ ????

Fernando Anto - 5 years, 3 months ago

4/2 * 6 = 12, but 2/4 * 6 = 3...

Paul Faithfull - 5 years, 3 months ago

yes its true but they gave only yes or no.. they should have another option for 'both'...!!!!!!!!!! :)

Fernando Anto - 5 years, 3 months ago

@Fernando Anto Yes, but then the word "ever" should be removed☺

Ashish Menon - 5 years, 3 months ago

6/4*8 = 12 and thats even!

Shivam K - 5 years, 3 months ago

@Shivam K It is asked if it is ever odd. It is even most times. But it is odd in one particularl case as explained by @Zandra Vinegar

Ashish Menon - 5 years, 3 months ago

What about y=5×3×16=240? Then we get 24/480×60=3.

Sarah Christin - 4 years, 12 months ago

There are infinitely many sets of 3 numbers for which this is true.

Tony Flury - 4 years, 11 months ago

the xy and z should be even but what u put is 5 and 5 is not a even no.

Veatriz Lausa - 5 years, 4 months ago

Veatriz - if you read what he wrote in full - yes z=5, but 2z is 10. What he is showing is that when the two's cancel out you can end up with odd numbers; remember that every even number is either 2 * an even number, or 2 * an odd number.

Tony Flury - 5 years, 4 months ago

try with 2^x, 2^y and 2^z -_- It will wrong if has a case make it wrong.

Hiển Nguyễn - 5 years, 4 months ago

could not understand 2nd step multiple of y

Debanjan Das - 5 years, 6 months ago

'y=even' ?

"even even=even,
even
odd=even, odd*odd=odd..."
Alwaya True..

Where am I wrong?

Mostafizur Rahman - 5 years, 6 months ago

You call the given answer bullshit - but you don't even actually address the problem as given. You are correct that any INTEGER multiplied by an EVEN is always EVEN - but you are assuming that the first division in the problem will yield an INTEGER - what if you have 2 4 6 \frac{2}{4} * 6 you would agree that all the values are EVEN - but the result is 3 which is odd]

Tony Flury - 5 years, 6 months ago

This was precisely my doubt whether the even number integer division has to be an INTEGER or it can be a Fraction ... if it becomes a Fraction then we are LOST.

Pranesh Mutalikdesai - 5 years, 5 months ago

@Pranesh Mutalikdesai Division is how many sets of things can be taken from a group, and it doesn't have to be an integer value, except in this case it is assumed that all variables are integers. EVEN÷EVEN is. E V E N E V E N \frac {EVEN}{EVEN} , which is a fraction comprised of integer values, so, using integer values 2 and 4, 2÷4 is 2 4 \frac {2}{4} , which is a fraction, which is to say how many sets of 2 can be taken from a group of 4. No one is bending rules here or doing anything else sneaky like turning an equation involving division into a fraction. The fact is that fractions are division!

And 2 4 \frac {2}{4} *6=3. ☺

Jeff Carter - 5 years, 4 months ago

@Pranesh Mutalikdesai Why is anyone lost if the division results in a fraction : that is simply mathematics. There is nothing in the question that stated that the division resulted in an integer, and it has been show that if the division results in a fraction then it is entirely possible for that fraction (when multiplied by an Even number) to result in an ODD result. That is simply Mathematics - elementary school maths.

Tony Flury - 5 years, 4 months ago

@Pranesh Mutalikdesai Then use the associative property if you aren't a fan of intermediate answers which are fractions, and read it as: (2*6)/4 = 3. But I think your problem more generally is that there aren't as general guidelines for determining even and odd solutions from the numbers in question during division, since the factors of a number are "cancelled" from one another rather than being added like in multiplication.

Andrew Trichak - 5 years, 1 month ago

Let a a be an even number a a 2 × a = 1 \dfrac{a}{a^{2}}\times a=1 and we know that 1 1 is an odd number, just for a 0 a \ne 0

Really nice point, didn't notice about it.

Darshan Baid - 5 years, 8 months ago

Nice set of cases!

Zandra Vinegar Staff - 5 years, 8 months ago

Okay great your solution is very good . But what do you thing now if I use different even number

like this 4/2 * 6 = 12?

Vubon Roy - 5 years, 8 months ago

But they're asking if is it possible, and it is for any a 0 a \ne 0 such that above

Hjalmar Orellana Soto - 5 years, 8 months ago
Tony Flury
Oct 3, 2015

Taking the prime factorisations of an EVEN number is always of the form 2 n × O D D 2^n \times ODD where n is a positive integer > 1 (We know that no even primes exist other than two)

so taking our original proposal : 1 E V E N E V E N × E V E N = O D D = 2 a × O D D 2 b × O D D × 2 c × O D D \boxed{1} \frac{EVEN}{EVEN} \times EVEN = ODD = \frac{2^a \times ODD}{2^b \times ODD} \times 2^c \times ODD

We can see that if 2 a + c b = 0 \boxed{2} a + c - b = 0 then all the powers of two will cancel out and we are left with 1.1 O D D O D D × O D D \boxed{1.1} \frac{ODD}{ODD} \times ODD

We also know that 3 O D D O D D \boxed{3} \frac{ODD}{ODD} must always be ODD assuming there is an integer result and that 4 O D D × O D D \boxed{4} ODD \times ODD must always be ODD

Assuming then that 2 \boxed{2} is true f r o m 1.1 O D D O D D × O D D = O D D × O D D = O D D from \boxed{1.1} \frac{ODD}{ODD} \times ODD = ODD \times ODD = ODD

There fore so long as you can cancel the twos completely i.e. 2 \boxed{2} is true then E V E N E V E N × E V E N = O D D \frac{EVEN}{EVEN} \times EVEN = ODD

Luke Nelson
Oct 2, 2015

Easy. Consider 6/4*2 = (6/2) = 3

Jerry Lopes
Oct 2, 2015

If there is no restriction on use of numbers than considering 4/8×2=1 which is odd.

Sarthak Sarroy
Mar 21, 2016

smallest even no. = 2,,, so, 2/4 x 6 = 3 is odd

Jamshad Ahmad
Oct 2, 2015

(2/4) x 6 is the simple pattern.

Multiply each digit with 3 and get infinite answers.

Ruth Dedman
Oct 1, 2015

If you make sure a smaller even number is in the numerator and a larger one in the denominator, you'll end up with a fraction. Multiply the fraction as necessary to create a whole odd number.

ex. 2 4 \frac {2}{4} x 2 = 1

Hm, not quite. If you picked 2 6 × A \frac{ 2 } {6} \times A , where A A is even, then you will still end up with an even integer.

Ultimately, it is about the number of powers of 2, and not just the size of the number.

Calvin Lin Staff - 5 years, 8 months ago

2/12*6=1 is not strictly powers of 2

Kelly Waters - 5 years, 8 months ago

What I meant was "Ultimately, it is about the number of powers of 2 that are in these numbers". IE, whether the expression is even or odd (given that it is an integer), depends on the number of powers of 2 that are involved.

I did not say "The final value must be a power of 2", or that "we can only use powers of 2".

Calvin Lin Staff - 5 years, 8 months ago
Matthew Kai
Feb 19, 2016

2÷4×2=1. 1 is odd whereas 2 and 4 are both even numbers.

Arpit Arora
Jul 6, 2016

2 x 2 / 4 = 1. Just Need to find a denominator to cancel out the power of 2 in the numerator, such that the final quotient is a whole number

David Heras
Jun 8, 2016

Yes. 2 8 4 = 1 \frac{2}{8}4=1 . Just arrange the number of factors of 2 appropriately.

6 * 2 /4 = 3, 10 * 2/4, 10*6/12, the examples are endless

Ksg Sarma
Mar 22, 2016

*let the two even numbers in numerator be 2 and the even in denominator be 4 * 2 4 \frac{2}{4} x 2 = 1

Andrew Anderson
Feb 28, 2016

6/4*2=3 fluff fluff fluff

Holly Teague
Feb 21, 2016

If the first two evens divide to give an integer then this integer will be even and the overall answer will be even but you could get a fraction ex. (6÷4)x2 = 3

Ashwin K
Feb 3, 2016

Simply tricky..

One example I got is (6/8*12) = 9.
Aaron Rodriguez
Feb 2, 2016

(2/4)*6=3. So I took an even integer, divided it by double of the integer, and multiplied the numerator by the sum of double of the integer and the difference between double the integer and the integer. In code speak: Int x; Int y = 2 * x; Int z = y + (y - x);

(x / y) * z;

Rod Patterson
Jan 29, 2016

I just thought about it for a few seconds, then wrote 2/4*6=3. Sometimes all you need is a little common sense.

Jeff Carter
Jan 26, 2016

Any fraction with a decimal equivalent of 0.5 multiplied by a whole even integer equivalent to two times any odd number will satisfy the conditions to produce the desired result. THere are many solution sets, though. Any fraction with a decimal equivalent of .25 multiplied by an even integer that is a multiple of 4 and an odd number will also work, e.g., 2 8 \frac {2}{8}* {12, 20, 28, 36, 44, 52, just to name a few} (and the answer will be that number divided by 4). Zandra Vinegar's explanation is the best, as it uses a formula to derive the solution.

Atiq Ahmed
Jan 24, 2016

6 x 4 / 8 = 3, in general (odd x even1) x (even2) / ( even3) = odd ,where even3 = even1 x even2

Aiden Huffman
Jan 23, 2016

(4/8)*2 = 1, which is odd by definition.

Take any fraction who when multiplied by 2, gives an odd number. Multiply the top and bottom of the fraction by two, the fraction remains the same but it is now even over even. Now multiply your fraction by 2, and you will have the odd number you planned to get at the start.

Luis Ortiz
Jan 9, 2016

Assuming its possible.

2k+1 = (2n/2z)*2y

2k+1 = 2ny/z

k+ 1/2 = ny/z

We find that,

If ny/z = (2w+ 1)/2, then you will always get odd numbers as result.

n,y = odd , z =1 ... Infinite possibilities

Dean Keith
Jan 6, 2016

2 divided by 4 multiplied by 10 = 5

Dylan White
Jan 6, 2016

2 / 4 * 2 = 0.5 * 2 = 1

Seokbong Seol
Jan 5, 2016

Don't think too much and take a=2,b=4,c=2, then ac/b = 1.

Youssef Hassan F
Dec 29, 2015

2/4 * 6 = 3

Sarthak Singh
Nov 29, 2015

it can be done using algebra

(2x/2y)*2z

or, (2xz)/y

so if we make y a multiple of 2 we will get the solution as odd

let y= (multiple of 2) and x = z = ( any odd number)

hence substituting values of x,y,z in (2x/2y)*2z we get (odd)

so ans is YES.

Connor Craig
Nov 17, 2015

6/4 x 2 = 3

Kyara Riguerra
Nov 16, 2015

An example is 2/4 * 6 which is equal to 3

Matt Sova
Nov 13, 2015

10/4=2.5. Multiply that by 2 and you get 5

Naveen K
Nov 8, 2015

2/4 (6) gvies 3

Zeeshan Ali
Nov 7, 2015

I just tried with the first three non negative even numbers 2, 4 and 6.

=> [2(EVEN) / 4(EVEN)] * 6(EVEN) = 3(ODD)

Aaysha Babu
Oct 23, 2015

6/4*2=3 6,4,2 are even nos

if we consider the formula to be (a/b)*c=x then how can we get an odd number? well the easiest way consider this is to think would be what can we multiply with an even number to make it odd? if an integer is multiplied by an even number you get an even number so we must be looking for a fraction so thinking about possible fractions 1/2 will work if multiplied by an even number that's not a multiple of 4 but is a multiple of 2 1/3 will work if multiplied by an even number that's not a multiple of 6 but is a multiple of 3 1/4 will work if multiplied by an even number that's not a multiple of 8 but is a multiple of 4 we can add whole numbers to the fraction without changing this behaviour basically if we multiply a fraction that is a multiple of the denominator we get a integer and of that set of numbers if they are twice as large and another member in the set we will generate a multiple of two

My initial thoughts were: Half of every other even number starting with 2 is always odd. Just make the denominator double the numerator and you get 1/2. Half of 2, 6, 10, 14, 18, 22....... all are odd.

Given (x/y) multiplied by z. For all even (or odd) integers x and y that are greater than 0, If y = 2x, Then x/y = 1/2. If z is even and z/2 = an odd integer, Then 1/2 of z is ALWAYS odd!

Yes you can get an odd number. Your 3 numbers can be any numbers (represented by x,y, and z here) that satisfy these conditions: x (any even number), y (where y = 2x), and z (where z is even and z/2 = any odd number)

Davy Ker
Oct 4, 2015

I had a fleeting moment of foolish assumption which went along the lines of "Well if both numbers are multiples of 2 then dividing one by the other must be a multiple of 2" which is nonsense. I realised that you can make "Even/Even" be any fraction you like, and came up with 18 20 × 10 = 9 \frac{18}{20} \times 10 = 9

To quote it very simply, 2/6x9 = 3 Which is odd. Problem solved!

Bhanu Dokiparthi
Oct 4, 2015

Simple. Let A=2,B=4 then C=6 then (2/4)*6=3 Hence we got odd number

Mamdouh Hamouda
Oct 4, 2015

Divisibility is something I am fascinated with and know much of its secrets

Dilip Luhar
Oct 4, 2015

take first even number=6, second even number=8 & third even number=4 (6/8)*4=3= odd

Wisnu Ops
Oct 4, 2015

If the dividends are 2 n × 2^n \times an-odd-number and 2 m × 2^m \times other-odd-number, then it works for any divisor that is 2 n + m 2^{n+m}

For example, if the dividends are 12 and 10, then it works if the divisor is 8.

12 × 10 8 = 15 \frac{12 \times 10}{8} = 15

The dividends:

12 = 2 2 × 3 12 = 2^2 \times 3

10 = 2 1 × 5 10 = 2^1 \times 5

The divisor:

8 = 2 3 = 2 2 + 1 8 = 2^3 = 2^{2+1}

Why it works that way?

Simply because odd × \times odd = = odd. So if you can cancel out all of the even factors (the 2's), you will get an odd number on the right hand side.

Khai Seox
Oct 4, 2015

Yes! For example: I have an odd number m m , and an even number n n , that three numbers are: n n , 2 k n 2^kn , and 2 k m 2^km

Jason Dworak
Oct 4, 2015

(2/4)x6 Since both an odd and even number times an even number is even, I thought the quotient must not be odd or even. That left a fraction.

Ayush Tiwari
Oct 4, 2015

2,4,6...(2÷4)×6=3..many such ways..

Joel Woods
Oct 4, 2015

2/4 x 2 = 1 or generally 2/4 x even = odd

Robert Underwood
Oct 3, 2015

(2/4 =.5 .5 x 2=1),

(2/4 =.5 .5 x 6=3),

(2/4=.5 .5 x 10=5),

(4/8=.5 .5 x 2=1),

(4/8=.5 .5x 6=3),

(6/12 = .5 .5x14=7)

(8/16=.5 .5x 18=9)

See the pattern? Any two even numbers where the dividend is twice the divisor will equal .5

.5 times every alternating even number (2, 6, 10, 14, 18......)* will yield an odd product

     * (4,8, 12, 16.....) will yield an even product

Any time you divide an even number that is a prime*2 by 4 and multiply by 2 you will get the prime back. You can also do this with any odd number. So there are infinitely many numbers this works for.

Garrett Stair
Oct 3, 2015

Any two even numbers when divided reduce to a fraction of 1/x where x is an even number can then be multiplied by x to get 1. 1 is an odd number. For example, 2/8 = 1/4 then multiply by 4 to get 1.

Ian Foster
Oct 3, 2015

I just thought of 2/4 * 2 (or any other way of getting a half)

Ritesh Singh
Oct 3, 2015

Umm......I guess we just need to remove the 2's from all the terms to make sure that only the odd term remains.Therefore 2,4,6 and other pairs where the denominator has equal number of 2's as the numerator will work.

Let's take 3 even nos like 12,8,6 then 12/8*6=9 proved....!!!!

Nelvin Cabatuan
Oct 2, 2015

your condintion that the numerator and denominator be divisible by 10 is not sufficient - or even neccessary - read some of the other solution and you will realise that.

Tony Flury - 5 years, 8 months ago

2/4*8=4 the result is even

Arun Nelakuditi - 5 years, 1 month ago
Iqbal Mohammad
Oct 2, 2015

let 'a' be an odd number and 'b' be an even number let 'c' = a x b, let 'd' = b x b then both 'c' and 'd' will always be even

so we have 3 even numbers b, c and d if evaluate (c / d) x b then

(c / d) x b = a , which is an odd number

Finn C
Apr 29, 2016

Really nice problem!

Nehemiah Osei
Oct 2, 2015

We can look at it this way

An even number multiplied by an even number is always even

And an even number multiplied by an odd number is even.

E v e n × E v e n = E v e n Even \times Even=Even

E v e n × O d d = E v e n Even \times Odd=Even

Equating the two equations,

E v e n × E v e n = E v e n × O d d Even \times Even=Even \times Odd

E v e n E v e n × E v e n = O d d \frac{Even}{Even} \times Even=Odd

This shows that it is possible.

N B NB : This is only true for even numbers that can be expressed as the product of an odd and an even number and at the same time be expressed as the product of two even numbers.

As is shown in the combined equation

But i got this result what do you thing about this ??

It is never true I show now two examples .

  1. 2/2 * 2 = 2
  2. 4/2 * 2 = 4
  3. 6/4 * 2 = 3 .

So it is never true

Vubon Roy - 5 years, 8 months ago

I am sorry for the misunderstanding I caused there.

I am actually trying to say that any even number that can be derived from the product of an even and an odd number, and at the same time be derived from the product of two even numbers could be rearranged to make it true.

I'll edit it. Thanks.

Nehemiah Osei - 5 years, 8 months ago

Unfortunately you cannot cancel terms like this. For example, it is possible for E v e n E v e n × E v e n = E v e n \frac{Even} { Even} \times Even = Even , and your solution would claim that is not possible.

Clara Blackstone - 5 years, 8 months ago

Lol.

Very sorry for the misunderstanding but thanks.

I'll edit it. Hopefully it will be clearer

Nehemiah Osei - 5 years, 8 months ago

I read all the solutions. I am glad so many discussions. But still I feel the question is not properly framed . Even/Even multiplied by Even need not be always Odd or Even. All examples, given above, shows the same . So, the solution CAN be ODD (some times) and NOT always EVEN The question should have been " Even/Even multiplied by Even can be Odd also." and definitely NOT as given in the problem " (Even/Even ) multiplied by Even = Odd" Here the " = " gives an indication that it always " True" but it is " not True" Thank you All

Madhusudhana Rao Sankarapu - 5 years, 8 months ago

@Madhusudhana Rao Sankarapu I understand your point but the question was

Can an even number, divided by another even number, times another even number ever equal an odd number?

The equation there was just supposed to be a visual representation of the possibility

Nehemiah Osei - 5 years, 8 months ago

@Nehemiah Osei Yes. I understand you point too. You are correct. In the statement/ question given in words is very clear. The answer is "True". But if you re-visit the equation in Colors alone gives a different impression Thank you very much

Madhusudhana Rao Sankarapu - 5 years, 8 months ago

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