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left handed or right?

by AIM TO CRACK GMAT » Tue Jan 22, 2013 11:56 pm
Some of the people in Town X are left-handed, some are tall, some are both, and some are neither. In Town Y, three times as many people are left-handed as are left-handed in Town X, three times as many people are tall as are tall in Town X, three times as many people are both as are both in Town X, but no one is neither. If the total number of people in Town X is four times greater than the total number of people in Town Y, which of the following could be the number of people in Town X who are neither left-handed nor tall?


A 23 B 39 C 72 D 143 E199
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by Anurag@Gurome » Wed Jan 23, 2013 1:02 am
AIM TO CRACK GMAT wrote:Some of the people in Town X are left-handed, some are tall, some are both, and some are neither. In Town Y, three times as many people are left-handed as are left-handed in Town X, three times as many people are tall as are tall in Town X, three times as many people are both as are both in Town X, but no one is neither. If the total number of people in Town X is four times greater than the total number of people in Town Y, which of the following could be the number of people in Town X who are neither left-handed nor tall?
Total number of people in either town = Tall + Left-handed - Both + Neither

Say, number of tall, left-handed, both and neither people in town X are T, L, B, and N, respectively.
Hence, the same in town Y are 3T, 3L, 3B, and 0, respectively.

Now, total number of people in X = total number of people in Y + 4*(total number of people in Y) = 5*(total number of people in Y)

So, (T + L - B + N) = 5*(3T + 3L - 3B)
--> N = 15*(T + L - B) - (T + L - B) = 14*(T + L - B) --> Multiple of 14

But, none of the options are multiple of 14.

Hence, I think "...total number of people in Town X is four times greater than the total number of people in Town Y..." simply means "...total number of people in Town X is four times the total number of people in Town Y..."

In that case, total number of people in X = 4*(total number of people in Y)

So, (T + L - B + N) = 4*(3T + 3L - 3B)
--> N = 12*(T + L - B) - (T + L - B) = 11*(T + L - B) --> Multiple of 11 --> Option D
Last edited by Anurag@Gurome on Wed Jan 23, 2013 3:21 am, edited 1 time in total.
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by AIM TO CRACK GMAT » Wed Jan 23, 2013 2:34 am
Anurag@Gurome wrote:
AIM TO CRACK GMAT wrote:Some of the people in Town X are left-handed, some are tall, some are both, and some are neither. In Town Y, three times as many people are left-handed as are left-handed in Town X, three times as many people are tall as are tall in Town X, three times as many people are both as are both in Town X, but no one is neither. If the total number of people in Town X is four times greater than the total number of people in Town Y, which of the following could be the number of people in Town X who are neither left-handed nor tall?
Total number of people in either town = Tall + Left-handed - Both + Neither

Say, number of tall, left-handed, both and neither people in town X are T, L, B, and N, respectively.
Hence, the same in town Y are 3T, 3L, 3B, and 0, respectively.

Now, total number of people in X = total number of people in Y + 4*(total number of people in Y) = 5*(total number of people in Y)

So, (T + L + B + N) = 5*(3T + 3L + 3B)
--> N = 15*(T + L + B) - (T + L + B) = 14*(T + L + B) --> Multiple of 14

But, none of the options are multiple of 14.

Hence, I think "...total number of people in Town X is four times greater than the total number of people in Town Y..." simply means "...total number of people in Town X is four times the total number of people in Town Y..."

In that case, total number of people in X = 4*(total number of people in Y)

So, (T + L + B + N) = 4*(3T + 3L + 3B)
--> N = 12*(T + L + B) - (T + L + B) = 11*(T + L + B) --> Multiple of 11 --> Option D
Hey anurag...Thanks for the solution...but will u plz clarify why have u added the Both group to the equation when u r suppose to be subtracting it? thanks a ton
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by Anurag@Gurome » Wed Jan 23, 2013 3:22 am
AIM TO CRACK GMAT wrote:but will u plz clarify why have u added the Both group to the equation when u r suppose to be subtracting it?
Thanks for pointing it out.
Edited the solution.
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by GMATGuruNY » Wed Jan 23, 2013 4:57 am
AIM TO CRACK GMAT wrote:Some of the people in Town X are left-handed, some are tall, some are both, and some are neither. In Town Y, three times as many people are left-handed as are left-handed in Town X, three times as many people are tall as are tall in Town X, three times as many people are both as are both in Town X, but no one is neither. If the total number of people in Town X is four times greater than the total number of people in Town Y, which of the following could be the number of people in Town X who are neither left-handed nor tall?


A 23 B 39 C 72 D 143 E199
One formula for overlapping groups:

T = Group1 + Group2 - Both + Neither

The big idea is to subtract the overlap. In the question above, there is an overlap between the left-handed people and the tall people. Thus, when we count all the left-handed people and all the tall people, the overlap -- the number who belong to both groups -- will be counted twice. So that we don't double-count these people, we need to subtract them from the total.

Let L = left-handed people in town X
Let T = tall people in town X
Let B = the people in X who are both left-handed and tall
Let N = the people in X who are neither left-handed nor tall

Town X:
X = L + T - B + N

In Y, there are 3 times as many left-handed people, 3 times as many tall people, and 3 times as many who are both:
Y = 3L + 3T - 3B

The total in X is 4 times the total in Y:
L + T - B + N = 4(3L + 3T - 3B)
L + T - B + N = 12L + 12T - 12B
N = 11L + 11T - 11B
N = 11(L + T - B).

Thus, the number of people in X who are neither left-handed nor tall must be a multiple of 11.

The correct answer is D.
Last edited by GMATGuruNY on Tue Aug 06, 2013 5:02 am, edited 1 time in total.
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by digvijay.rajput » Tue Aug 06, 2013 3:22 am
GMATGuruNY wrote:
The total in X is 4 times the total in Y:
L + T - B - N = 4(3L + 3T - 3B)
L + T - B + N = 12L + 12T - 12B
N = 11L + 11T - 11B
N = 11(L + T - B).
Nicely explained...
There is a minor correction.
The first step of the solution should be :-
L + T - B + N = 4(3L +3T - 3B)
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