If 3^a - 3^(a-1) = 162 then a(a-1) = Choose one:
A) 12
B) 16
C) 20
D) 30
E) 81
It seems like you were really close but you solved for a - 1 instead. I am curious - how did you reason through the question? Perhaps you figured the answer has to be in the form of a(a -1), e.g. (3)(4) = 12. Even then, had you figured a has to be a little bigger (plugging in 4 for a gives you 81 which is too low), So when you reasoned the answer to be 4 you may have plugged the 4 in the (a - 1) exponent place.   Again, a quick plugging in should get you (20) 20 as, the only other answer with consecutive integers as factors is far too big.
<result>C</result>
If 3^a - 3^(a-1) = 162 then a(a-1) =