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Good one!

by GmatKiss » Sun Oct 16, 2011 10:59 am
Data Sufficiency: The number A is a two-digit positive integer; the number B is the
two-digit positive integer formed by reversing the digits of A. If Q = lOB - A, what
is the value of Q?

(1) The tens digit of A is 7.
(2) The tens digit of B is 6.
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by shankar.ashwin » Sun Oct 16, 2011 11:19 am
B IMO

10x + y = A
10y + x = B
100y + 10x = 10B

10B - A = 99y.

In (2) y is given, so sufficient
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by neelgandham » Sun Oct 16, 2011 6:46 pm
GmatKiss wrote:Data Sufficiency: The number A is a two-digit positive integer; the number B is the
two-digit positive integer formed by reversing the digits of A. If Q = lOB - A, what
is the value of Q?

(1) The tens digit of A is 7.
(2) The tens digit of B is 6.
A = 10m + n
B = 10n + m
Q = 10(10m+n) -(10n+m) = 99n

So, we need either the units digit of A or the tens digit of B to answer the question.

Option 1) Blah Blah
Option 2) Yes

Answer : B
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by Anurag@Gurome » Mon Oct 17, 2011 2:55 am
GmatKiss wrote:Data Sufficiency: The number A is a two-digit positive integer; the number B is the
two-digit positive integer formed by reversing the digits of A. If Q = lOB - A, what
is the value of Q?

(1) The tens digit of A is 7.
(2) The tens digit of B is 6.
A = 10x + y
B = 10y + x
Q = 10 * (10y + x) - 10x - y = 99y

(1) The tens digit of A is 7, but that is NOT sufficient.

(2) The tens digit of B is 6, which gives us the value of y; SUFFICIENT.

The correct answer is B.
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