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Source: — Data Sufficiency |
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by tpr-becky » Fri Aug 05, 2011 10:28 am
if A + B = CD and each letter represents a POSITIVE digit that means that two single digits add up to a double digit (none can be 0)

1) if D=1 then we have to add up to 11 (can't add up to 21 becuase we only have single digits). however you can get 11 with 9 + 2, 8+3, 7+4 etc... so we can't tell what A and B would be.

2) if B = 2 then the sum must again be 11 - If we add 2 to a single digit number the only two digit numbers we can get are 10 and 11. But D can't be 0 based on the definition in the question stem. Therefore A must be 9. and your answer is B.
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by ofirzg » Fri Aug 05, 2011 10:32 am
Thanks Becky!

For some reason the test said it was C rather than B, but they based their answer on the assumption that 0 can count as a positive integer, which is probably false.
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by gmatboost » Fri Aug 05, 2011 11:10 am
It is definitely a false assumption. Then again, I have never seen the phrase "positive digit" used in any official GMAT materials.

I would be careful about using practice questions from a source that makes mistakes of that sort and uses unusual terms.
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by gmatblood » Fri Aug 05, 2011 12:57 pm
IMO: C
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by akhilsuhag » Fri Aug 05, 2011 1:03 pm
The Answer will be C.

Becky has carried information from statement 1 to 2 and thus gotten B as the answer. If you look at statement 2 in isolation then it is not sufficient. Bur together they are.

I hope i am right!!

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by tpr-becky » Fri Aug 05, 2011 1:41 pm
I did not carry information from statement 1 over.

the question clearly stated that A, B, C and D are each positive digits - that means they each must be a digit from 1 to 9 (zero is not positive and 10 is a 2 digit number).

A and B are both single digit numbers adn the highest you can add to will be 18 (9+9)

if B = 2 then A must be either 8 or 9 to get a 2 digit sum (10 or 11). However if D is a positive digit D cannot be 0 so the sum must be 11, which means that A must be 9.
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