Data Sufficiency (DS) | Re: The only gift certificates that a certain store sold

For these diophantine equations, it is actually possible to reduce the question pretty succinctly with algebra. Some people don't need to do that, and it does take a few extra seconds, but if you're interested this is how I didit.

Given:

100(A) + 10(B) = ?
A + B =20

Statement 1:

100(A) + 10(B) = (1650, 1800) --> divide the whole equation by 10 to simplify.
10(A) + B = (165, 180) --> use the given information to substitute in for A.
10(20-B) + B = (165, 180)
200 - 9B = (165, 180) -->
...

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