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digits and decimals

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by Gurpinder » Sat Aug 14, 2010 7:22 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.

OA: [spoiler](B)[/spoiler]

My automatic response to this one was C. Why is that wrong!!!!

Please explain how to approach this problem!
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Source: — Data Sufficiency |
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by kvcpk » Sat Aug 14, 2010 7:40 am
Gurpinder 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.

OA: [spoiler](B)[/spoiler]

My automatic response to this one was C. Why is that wrong!!!!

Please explain how to approach this problem!
A = 10X+Y
B=10Y+X

Q = 100Y+10X-10X-Y
Q=99Y
(1) The tens digit of A is 7.
implies X=7
.. No info about Y
INSUFF
(2) The tens digit of B is 6.
Y=6
Hence 99Y can be calculated.
SUFF

pick B.
Last edited by kvcpk on Sat Aug 14, 2010 10:29 am, edited 1 time in total.
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by 7806 » Sat Aug 14, 2010 10:08 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.

for 2.. say B=6x so A=x6.
Q=10B-A= 6x0-x6= 594.
so The answer is B..!!
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by 7806 » Sat Aug 14, 2010 10:10 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.
for 1. A=7x B=x7 Q=x70-7x = .....x may be anything from 0 to 9... so , insufficient.
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by gmatmachoman » Sat Aug 14, 2010 10:17 am
7806 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.
for 1. A=7x B=x7 Q=x70-7x = .....x may be anything from 0 to 9... so , insufficient.

Fantastic!!
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