[Math Revolution] Practice "Math Questions of the Day"

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To help you sharpen your math skills and hit your target score of Q49-51, we are sending you 4 math questions (2 DS, 2 PS) and solutions regularly.
These questions are the types of questions appearing in GMAT exam frequently.

Please Click the link for solutions.


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by ParryB » Mon Aug 05, 2019 3:32 pm
For question #1, why is the answer C and not B?
A77A is a multiple of 9 so that means A77A is divisble by 9
=> A+7+7+A is divisible by 9
=> 2A+14 is divisible by 9
=> 2(A+7) is divisible by 9
=> 2 is not divisible by 9 so (A+7) has to be divisible by 9
=> Range for A is from 0-9 and only 2 can be the valid solution for (A+7) to be divisible by 9. This is an unique answer just as you have mentioned in the solution. So, why is statement 2 alone not sufficient?