Multiples 3 digit numbers

If both M , N M, N are 3 digit numbers and their ratio, M N \frac M N is an integer. What is the largest possible value of M N \frac M N ?

9 11 8 10

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15 solutions

First, note that 9 9 is a valid possibility when, for example, 9 111 = 999 9*111 = 999 .

Any number from 10 10 and beyond, when multiplied by a 3 3 -digit number becomes a number greater than or equal to 1000 1000 , and so N N would be a 4 4 -digit number which would not meet the problem's requirements.

The solution that I was thinking of was 900 100 = 9 \frac{900}{100} = 9 , but of course there are numerous possibilities.

Chung Kevin - 6 years, 2 months ago

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How not 10? The largest possible imo should be 999/100 = 9.99 = 10

Hassaan Islam - 6 years, 2 months ago

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9 is the largest integer that is smaller than 9.99.

Chung Kevin - 6 years, 2 months ago

he said it is integer

Shivashankar Goud - 6 years, 2 months ago

That's exactly what I did. The greatest three digit number is 999 and the lowest 100. I feel the correct answer is 10. 999/100 = 9.9 which rounds up to 10! Just saying :)

Chelsea Sanchez - 6 years, 2 months ago

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@Chelsea Sanchez In repsonse to both Chelsea and Hassaan, I was going with that too, until I reread the question to see that the answer had to be an integer. Since the question did not allow rounding and 9.99 would not be an integer, the answer had to be 9 as the largest integer that could be created by the stipulations given.

Keith Abramowski - 6 years, 2 months ago

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@Keith Abramowski Oh. Whoops! Many thanks to Daniel and Keith for clarification. :)

Chelsea Sanchez - 6 years, 2 months ago

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@Chelsea Sanchez Actually, now that I think about it, ANY problem given these parameters would come out to "9". If M/N is an integer and both M and N are 5 digit integers, it would still be "9" = 90000/10000 = 9

Keith Abramowski - 6 years, 2 months ago

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@Keith Abramowski It always will be. A factor of 10 requires, well, a factor of 10.

Christopher Altis - 6 years, 2 months ago

@Keith Abramowski That's correct! You should post the 5 digit version of this problem.

Chung Kevin - 6 years, 2 months ago

@Chelsea Sanchez Still not an integer. Sure you'd be right if it asked to round to the nearest whole number, but 9.99999<10. So therefore your reasoning is invalid for this particular question.

Daniel Schnoll - 6 years, 2 months ago

i did it the same way bro.. Nice solution!!!!!!!

samuel ayinde - 6 years, 2 months ago

If so, den y nt 8????

Harish Hari - 6 years, 2 months ago

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We are looking for the largest integer value of M N \frac M N , we are not looking for the second largest or third largest or so on.

Pi Han Goh - 6 years, 2 months ago
Samuel Ayinde
Mar 18, 2015

observe that when you multiply a 3digit number by 10, you get a 4digit number. Therefore, the largest possible value of m n \frac{m}{n} is 9 9

Great! The 4 digit observation greatly reduces the work that has to be done :)

Chung Kevin - 6 years, 2 months ago
Rishikesh Roshan
Mar 19, 2015

The biggest 3 digit no=999 The smallest 3 digit no=100 999/100=9.99 Hence, the largest possible value is 9

Right, that's another way to show that the largest value is < 10.

Chung Kevin - 6 years, 2 months ago

Clear explanation

Prasanna Boyidi - 6 years, 2 months ago

obviously I agree with his solution

mathslord victor - 4 years, 4 months ago
Jordan Smith
Mar 25, 2015

M and N are both 3 digit numbers, so they can range from 100 to 999. The highest possible number for the equation would be 999/100 but that will not equal an integer so you will increase the number to 999/111 and that will equal 9

Perfect! It's rare to see someone from South Africa ,so welcome to the Brilliant community!

Chung Kevin - 6 years, 2 months ago
Xi Huang
Mar 26, 2015

100 9=900 this is an example but you can go farther Since 100 is the smallest 3didgit number, 100 10=1000. 1000 is a four digit number. Therefore 9 is the highest

That is an example. How do you know that we cannot go further?

Chung Kevin - 6 years, 2 months ago

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Oh. I forgot to post the second part. It's: Since 100 is the smallest 3didgit number, 100*10=1000. 1000 is a four digit number. Therefore 9 is the highest

Xi Huang - 6 years, 2 months ago

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Yes. Can you add that to your solution? You can edit it by clicking on the edit button.

Chung Kevin - 6 years, 2 months ago
David Stigant
Mar 26, 2015

100<=M<1000 so 2<=logM<3 and 100<=N<100 so 2<=logN<3 or -3<-logN<=-2. Adding theses inequalities gives -1<logM-logN<1 or -1<log(M/N)<1 or 1/10<M/N<10. Since M/N is an integer,1<= M/N<=9. We can easily find examples of M/N=9 (M=900, N=100), but we will search in vain to find an example where M/N=10.

Christian Ryan
Mar 26, 2015

The greatest 3 digit integer is 999 and the smallest is 100. However, because we are looking for integers and also dividing by 100 we know that we can only use exact three digit multiples of 100; the greatest of those multiples being 900. Therefore,

900/100 = 9

Nicely done!

Chung Kevin - 6 years, 2 months ago
Brock Brown
Mar 18, 2015

Python 2.7:

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biggest = 0
for m in xrange(100,1000):
    for n in xrange(100,1000):
        if m % n == 0:
            if m/n > biggest:
                biggest = m/n
print "Answer:", biggest

That is beautiful claps

Daniel Schnoll - 6 years, 2 months ago

xrange(100,999)

Waqi Ur Rehman - 6 years, 2 months ago

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Actually, the two parameters for xrange are start and stop ; the output will never include stop . Try it.

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start = 1
stop = 1
for i in xrange(start, stop):
    print i
# outputs nothing

I know it's a weird rule, but I think it's designed so that if you use xrange(n) you can have the number of iterations be exactly n. For example...

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for i in xrange(10):
    print 'output'

...will print 'output' 10 times. The values of i would be [0,1,2,3,4,5,6,7,8,9].

Brock Brown - 6 years, 2 months ago
Viki Zeta
Jun 3, 2016

Pythonic solution

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'POSSIBILITY ESTIMATOR'

nos = range(100, 1000)
nos2 = range(100, 1000)
possible = list()

for i in nos:
    for j in nos2:
        if i % j == 0:
            possible.append(i / j)

print list(set(possible))[-1]

Nilesh Raut
Dec 25, 2015

Largest 3 digit no 999 Smalest 111 to have integer ratioo 999/111=9

Kay Vicente
Dec 6, 2015

Divide the largest 3-digit number by the smallest 3-digit number. So, 999÷100=9.

In order to get a possible answer I just devided biggest 3 digit number possible and smallest three digit number possible. Thus, 999/111 =9

Vivian Liang
Jun 29, 2015

Choose the highest possible 3 digit whole number and substitute it for M. So M=999. Then, you need to find what is N. Easy. Just divide 999 by 9. Why 9 for N? Because it's probably the only whole number you can use that will divide 999 without turning the quotient into a decimal number that will keep it a 3 digit number.

M=999 N=111
M/N=999/111

999/111=9

Aman Kharbanda
Mar 26, 2015

M is 999, and n can be 111

Moderator note:

You have only shown that M N = 9 \frac M N = 9 is possible, and you haven't shown that 9 9 is the maximum value nor did you explain why you chose the values of m , n m,n specifically.

But, why can't the answer be 10?

Chung Kevin - 6 years, 2 months ago
Amilcar Rodriguez
Mar 25, 2015

I just multiplied 3 times 3

Moderator note:

This solution has been marked wrong because it fails to show any connection to the problem.

Hm, can you explain why?

Chung Kevin - 6 years, 2 months ago

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