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by nidhis.1408 » Wed Jun 27, 2012 7:13 am
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 =10B - 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 Anurag@Gurome » Wed Jun 27, 2012 9:10 am
nidhis.1408 wrote: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 =10B - A, what is the value of Q?

(1) The tens digit of A is 7.
(2) The tens digit of B is 6.
Say, the unit's digit and ten's digit of A are x and y respectively.
Hence, A = (10y + x) and B = (10x + y)
Hence, Q = (10B - A) = (100x + 10y - 10y - x) = 99x

Therefore, we need to know x, i.e. the unit's digit of A or tens digit of B.

Obviously only statement 2 is sufficient to answer the question.

The correct answer is B.
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