The Repetitious Sum

Logic Level 2

X Y Z X Y Z + X Y Z Z Z Z \begin{array} { l l l } & & & X & Y & Z \\ & & & X & Y & Z \\ &+ & & X & Y & Z \\ \hline & & & Z & Z & Z \\ \end{array}

If X , Y , X, Y, and Z Z are distinct digits, then what is the value of X × Y × Z ? X \times Y \times Z ?


The answer is 40.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

23 solutions

Mehul Arora
Jun 28, 2015

X Y Z + X Y Z + X Y Z = Z Z Z \overline {XYZ}+\overline {XYZ}+\overline {XYZ}=\overline {ZZZ}

The Last Digit, That is Formed By adding 3 Z s Zs together, Is Z.

The only possible number Where this is possible is 5. Any number ending with 5 when added 3 times , will have the unit's digit as 5

So, Z = 5 Z=5

Now, X Y 5 + X Y 5 + X Y 5 = 555 \overline {XY5}+\overline {XY5}+\overline {XY5}=555

3 × X Y 5 = 555 3 \times \overline {XY5}=555

X Y 5 = 185 \overline {XY5}=185

X = 1 , Y = 8 , Z = 5 X=1,Y=8,Z=5

1 × 8 × 5 = 40 1 \times 8 \times 5= \boxed {40}

Moderator note:

Well done.

There is a simpler way to do it. When we know that Z = 5 Z=5 , so Z Z Z = 555 ZZZ=555 . Just divide 555 555 by 3 3 to get X Y Z = 185 XYZ=185

Vighnesh Raut - 5 years, 11 months ago

Log in to reply

awesome bro keep it up i solved by using above method

Praveen Reddy - 5 years, 7 months ago

That's not a simpler way -- that is exactly the same way.

Paul Alberti-Strait - 4 years, 11 months ago

Mathematically representing,

3 Z Z ( m o d 10 ) 3Z \equiv \ Z \ (mod \ 10)

General solution is 5 + 10 k 5 \ + \ 10k

Thus, the smallest positive solution is 5 5 .

Now 3 Y + 1 5 ( m o d 10 ) 3Y \ + \ 1 \equiv \ 5 \ (mod \ 10)

General solution is 8 + 10 k 8 \ + \ 10k

Smallest solution is 8 8

3 X + 2 5 ( m o d 10 ) 3X \ + \ 2 \equiv \ 5 \ (mod \ 10)

General solution is 1 + 10 k 1 \ + \ 10k

Smallest solution is 1 1

So the number is 185 185

Hence, the product is 40 \boxed{40}

Kunal Verma - 5 years, 11 months ago

0 must be a correct answer. 0 is a digit, and nothing says that X, Y, and Z must be different digits.

Ivan Ketler - 5 years, 7 months ago

Log in to reply

the question says distinct and distinct means different

Youssef Hassan F - 5 years, 4 months ago

What a ques!!

Paras Jain - 5 years, 5 months ago

Your first statement is false: There are 2 solutions 3xZ = 10N+Z : Z = 0 and Z = 5. With Z=0, ZZZ = 000 or simply 0. The only M where 3xM = 0 is 0, which means that X=Y=Z=0. But X, Y, and Z must be distinct so Z = 0 is not a VALID solution. So Z must be 5. ZZZ is then 555. XYZ+XYZ+XYZ =555 -> XYZ x 3 = 555 -> XYZ = 555/3 = 185. XxYxZ -> 1x8x5 = 40.

Lars Wegge Andersen - 2 years, 10 months ago

Great explanation, thank you! 🇦🇷

Fran Rodriguez - 1 year, 7 months ago

240 is also correct, Right ?

Himanshu Oswal - 1 year, 3 months ago

Yo @Mehul Arora

Isn't this the question trending on whatsapp ??

Vaibhav Prasad - 5 years, 11 months ago

Log in to reply

Lol, I didn't know This AT ALL.

I am Not on Whatsapp :P :P

Mehul Arora - 5 years, 11 months ago

Log in to reply

You are on Whatsapp HAHA

Nihar Mahajan - 5 years, 7 months ago

Log in to reply

@Nihar Mahajan Yeah hahaha

Mehul Arora - 5 years, 7 months ago

I solved this question 4 4 times this year ...

Nihar Mahajan - 5 years, 11 months ago

Should be 3z=z-10

robert sallette - 5 years, 9 months ago

thank you for explaining the answer so well

Ayush Jain - 5 years, 7 months ago
Ethan Godden
Jun 29, 2015

Z+Z+Z has its last digit equal to Z. The only solution to that is Z=5. Carry a 1 over to the Y column because 3(5)=15

Y+Y+Y+1 has its last digit equal to 5. The only solution to that is Y=8. Carry a 2 to the X column because 3(8)+1=25

X+X+X+2 has to be a one digit number and has to equal 5. The only solution to that is X=1

Moderator note:

Great! With cryptogram problems, having the correct order of approach would simplify it. Working from the right tends to be helpful, because we can keep track of carry-overs.

I did this :-)

Aditya Pahuja - 5 years, 1 month ago

Did this one too, though realised it was overkill when looking at Mehel's answer :p As soon as we knew Z=5, 3x=555, x=185, 1 8 5=40. Done.

Kyle Manley - 4 years, 10 months ago

I too solved this way

ankit raj - 4 years, 8 months ago
Gampa Varun
Jul 2, 2015

5 is the only single digit number which when multiplied by 3 results in a number whose units digit is 5 hence z=5 now therefore zzz = 555 and we know that xyz X 3 =zzz therefore xyz X 3=555 which implies that xyz = 555/3 = 185. Hence x=1 y=8 and z=5 therefore x X y X z=40

Inga Velo
Jul 3, 2015

So, firstly we have

Z × Z × Z = a × 10 + Z Z \times Z \times Z = a \times 10 + Z , where a is non-negative digit

If a = 0, then Z = 0. Wrong.

If a = 1, then Z = 5. Good.

If a = 2, then Z = 10. Wrong.

So Z = 5 \boxed{5}

Next, we have:

Y × Y × Y + 1 = b × 10 + Z Y \times Y \times Y + 1 = b \times 10 + Z , where b is non-negative digit and 1 comes from 5 + 5 +5 = 1 \boxed{1} 5

If b = 0, Y = 4/3. Wrong.

If b = 1, Y = 14/3. Wrong.

If b = 2, Y = 8. Good.

If b =3, Y = 34/3>10. Wrong.

So Y = 8 \boxed{8}

Finaly, we have:

X × X × X + 2 = c × 10 + Z X \times X \times X + 2 = c \times 10 + Z , where c is non-negative digit and 2 comes from 8 + 8 +8 +1 = 2 \boxed{2} 5

If c = 0, X = 1. Good

If c = 1, X = 13/3. Wrong.

if c = 2, X = 23/3. Wrong

If c = 3, X = 33/3 > 10. Wrong.

So X = 1 \boxed{1}

Then we have X × Y × Z X \times Y \times Z = 1 × 8 × 5 1 \times 8 \times 5 = 40 \boxed{40}

Zu'Qa Zooz
Jul 2, 2015

The game here is a game of digits ,right? if we try to do this sum : 3Z = Z+10a : where a is a normal number {1,2,3,4....} whatever. we will find that the only possible solution for it is that Z = 5 and Z = 0. and we start solving on those 2 ways: Z = 0 then 3Y+0=Z+10b. where be is in the same domain of a. where Z = 0 , 3Y = Z+ 10b, and the b is determined logically. then we find that Y = Z/3 + 10b. the digit Y = the digit Z and that's unaccepted, so we move on in the other way where Z = 5: then Z*3 = Z+10a , a = 1.

lets do what we did in elementary school: 1 + 3Y = Z+10b, then 3Y = 4+10b. lets do what we did in the top, and multiply 3 by each number between 0 and 9 and see which resultant number has the digit "4" as its last digit. and the only possible number we used that gets this result is number "8" and the result is 24. then 24 = 4 + 10b > b=2.

the same elementary thingy, 2 + 3X= Z + nothing because we have no more digits then 2 + 3X = 5 > 3X = 3 > X=1.

^_^

What, when added to its self, is its self? That is five. Divide by three to get X and Y

Moderator note:

Why not Zoidberg, aka 0? We should still add a sentence explaining that the solution 0 has been rejected.

Great observation that once we found Z Z , we can just take X Y Z = Z Z Z 3 XYZ = \frac{ZZZ}{3} .

Jason Khuu
Jul 1, 2015

XYZ} + XYZ + XYZ = ZZZ Therefore we can say 3 b o x e d X Y Z boxed{XYZ} = b o x e d Z Z Z boxed{ZZZ} Given that X, Y and Z are single digit positive integers, we can say:

300X + 30Y + 3Z = 100Z + 10Z + Z

300X + 30Y = 108Z

100x + 10Y = 36Z

As all digits are integers, we know the variables:

36Z > 110 and 36Z </= 324 thus 110 > 36Z >/= 324

36Z must be a multiple of 10, only value for that within the range 110<36Z</=324 is 180 where Z = 5 , therefore as X and Y are single digit positive integers (not 0, negative or more than 9) X=1 and Y=8

Therefore XYZ =1 x 8 x 5 = 40

William Feild
Oct 24, 2015

If X could equal Y and Z, then the product could also be 0 because X, Y, Z = 0 satisfies the summation as well.

Amos Tan
Jul 3, 2015

Z+Z+Z = Z , only 5 , bcaz cant be 0 , when Z = 5, 3(XYZ) =ZZZ , 555=ZZZ , ZZZ/3 = XYZ , 555/3 = 185 , 1(8(5)) =40

Noel Lo
Jul 1, 2015

From the ones column, we deduce that

3 Z = 10 k + Z 3Z = 10k + Z where k k is a non-negative integer.

2 Z = 10 k 2Z = 10k

Z = 5 k Z = 5k .

Since Z Z is single digit, 5 k 5k is at most 9 9 so k k is at most 1.8 1.8 . Since k k is positive, k k is strictly greater than 0 0 so the only possible integer for k k is 1 1 so that Z = 5 Z = 5 .

Hence X Y Z = 555 3 = 185 XYZ = \frac{555}{3} = 185 and X × Y × Z = 1 × 8 × 5 = 40 X \times Y \times Z = 1 \times 8 \times 5 = \boxed{40} .

Zoba Kemo
Dec 7, 2019

z+z+z=nz, 3y+n=rz. 3x+r=z,, n and r are carry So: z=0 or, z=5,, Then z=5, n=1,, 3y+1=r5,, Y=8,, (8×3)+1=25,, r=2,, 3x+2=5,, X=3

Rod Hutchings
Sep 27, 2017

From the 1's digit, Z + Z + Z = Z(mod 10), so subtracting Z from each side gives 2Z = 0(mod 10), so either 2Z = 0, or 2Z = 10. (2Z = 20 or 30, etc, yields a value of Z larger than a single digit). So either Z=0 or Z=5, but since Z is a leading digit in the result, it cannot be 0. Hence Z = 5.

Now, if N = X Y Z N = \overline{XYZ} , then it follows from the sum that 3N = 555, so N = 185. Hence, X=1, Y=8, and Z=5. Hence, XYZ = (1)(8)(5) = 40.

Eric Lucas
Jun 5, 2017

From the 3s multiplication table:

The only number Z such that 3Z ends in Z is Z = 5.

Then, carrying the 2, 3Y + 1 ends in 5, or 3Y ends in 4. The only such single-digit number is Y = 8.

Again, carrying the 2, 3X + 2 = 5, so X = 1.

5 * 8 * 1 = 40.

Shanly Krismas
Dec 3, 2016

We must find a digit Z so that 3xZ has a unit digit of Z. Thus, Z=5 is the only solution. Carry a 1 over to the Y column because 3x5=15. That means 3x X Y \overline {XY} +1=55. Thus, 3x X Y \overline {XY} =54, so X Y \overline {XY} =18. X=1 and Y=8 1x8x5=40, 40 is the answer.

The concept of 5 where in any number is multiplied with 5 is equal to 0 or 5 at the end of the digit. So by multiplying 3(because we have 3 digit) by 5 we can have 15 at the end of the digit Z. And substitute Z to 5. Our equation will be (XY5) x 3 = 555. X will always be 1 because if we consider it to be more than 1 if you add it up it will not be 5 it will be more than 5. We have 3 and we have 5. 3 + 5 = 8 for Y. 1 x 8 x 5 = 40

Matthew Venard
Aug 3, 2016

X Y Z 3 = Z Z Z \overline{XYZ}*3=\overline{ZZZ}

And we know that the only possible number in which the condition Z 3 = Z Z*3 = Z in the tens place is for Z = 5 Z=5 .

Therefore, we can use the equation 555 3 \frac{555}{3} to get the value of X Y Z \overline{XYZ} which is 185.

Multiplying each digit results in a product of 40 \boxed{40} .

Ellis Wright
Jun 30, 2016

The last number has to 5, so the answer must be 555. 555/3= 185 so 1 8 5= 40

Gareth Adamson
Jun 11, 2016

Z has to equal 5 (only non-zero one-digit number that equals itself when multiplied by 3)

XYZ + XYZ + XYZ = 555

3(XYZ) = 555

XYZ = 185

1 x 8 x 5 = 40

Youssef Hassan F
Jan 23, 2016

z + z+z= z(in unit) the only no. < 10 that has this properties is 5 so z+z+z=15 so there is a carry up 1 here so y+y+y+1=5(in unit) so y+y+y=4(in unit) the only no. < 10 that has this properties is 8 so y+y+y=24 so we have a carry up 2 so x+x+x+2=5 and have no tens so x+x+x=3 so 3x=3 so x=3/3=1

now x y z=1 5 8=40

Raymond Julianto
Oct 28, 2015

Z is a number when multiplied by 3 is Z it self. What could it possibly be? Yes, 5 just 5.

The answer is ZZZ , which is 555.

Which hundreds could be multiplied by 3 and not exceed 555? Yes, just 1

We now here get X=1 Z=5

What could possibly the other number be?

Since it's 500+, then we should choose number >6

We can try 7 and get 175*3=525 which is incorrect

Next we can try 8 and get 185*3=555 which is correct.

Then we get X,Y,Z are 1,8 and 5 respectively

X * Y * Z= 1 * 8 * 5 = 40

Chris Yuen
Oct 25, 2015

While I got the product 40 for this problem, the product 0 is also mathematically correct because it is not obligatory to assume x, y, and z are unique digits.

Joel Shah
Oct 25, 2015

XYZ + XYZ + XYZ = ZZZ, 3 * XYZ = ZZZ, 3 * Z = Z + Something * 10 Z = Something * 5 Z = 5 3 * XYZ = 555 XYZ = 185 X * Y * Z = 1 * 8 * 5 = 40

Here,

  1 8 5

  1 8 5

  1 8 5

  5 5 5

So, 1 * 8 * 5 = 40

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...