While this question is a couple of years old, it DOES showcase a particular Exponent-rule 'concept' that you're almost certain to face on the Official GMAT: re-writing a "base" when dealing with exponents...
Any time the 'base value' is a positive integer that is not 1 and is not prime, it has the potential to be rewritten...
Here, we're dealing with 27^5....
27 = (3)(3)(3) = 3^3, so we can re-write that base as...
Here, we have a 'power to a power', which means we can multiply the two exponent values....
(3)(5) = 15
So...(3^3)^5 = 3^15
This is just one of several Exponent rules that you need to know for Test Day. While you're not going to be tested on every rule, having the overall knowledge and the ability to manipulate the numbers will help you to pick up the handful of Exponent rule questions you'll face on the GMAT.
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