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by KapilKapoor » Thu Sep 20, 2012 5:12 am
Hi all,

S is a set of 2 digit natural numbers. A pair of (P,Q) to be selected from S, so that at-least one digit is common?

The answer is
Total-No common = At least one common
81*81-9*8*8*7 = 2529

I'm getting the answer as 90*90-9*8*8*7 = 4068

I don't understand the concept of 81*81.

Please help.

Thanks & Regards,
Kapil
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by Jim@StratusPrep » Thu Sep 20, 2012 7:13 am
They are subtracting out numbers that have both digits the same 11, 22, 33...

This question in general is pretty vague.
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by GMATGuruNY » Thu Sep 20, 2012 8:04 am
I posted a solution here:

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