Problem Solving

boomgoesthegmat wrote:The positive two-digit integers x and y have the same digits, but in reverse order. Which of the following must be a factor of x + y?

A) 6
B) 9
C) 10
D) 11
E) 14

OA: D

The question asks is to find what MUST be true.

So, a quick and simple solution is to TEST some values. If a statement turns out to be FALSE, we can eliminate that answer choice.

Let x = 12 and let y = 21
So, x + y = 12 + 21 = 33

Now check the answer choices.
A) 6 is not a factor of 33. ELIMINATE A
B) 9 is not a factor of 33. ELIMINATE B
C) 10 is not a factor of 33. ELIMINATE C
D) 11 IS a factor of 33. KEEP D
E) 14 is not a factor of 33. ELIMINATE E

Answer: D

Cheers,
Brent

Hi boomgoesthegmat,

This question is perfect for TESTing VALUES (as Brent's approach shows). One of the great aspects about this question is that there are a variety of options that you can use to find the correct answer.

Brent ended up using 12 and 21, for a total of 33

But you could also use...
25 and 52, for a total of 77
13 and 31, for a total of 44
23 and 32, for a total of 55
Etc.

Final Answer: D

GMAT assassins aren't born, they're made,
Rich