mikemcgarry
If A is the initial amount put into an account, R is the annual percentage of interest written as a decimal, and the interest compounds annually, then which of the following would be an expression, in terms of A and R, for the interest accrued in three years?
(A) \(A(R)^3\)
(B) \(A(R + R^3)\)
(C) \(A(3R + 3R^2 + R^3)\)
(D) \(3A(R)^3\)
(E) \(3A(R + R^2 + R^3)\)For a discussion of
simple vs. compound interest, as well as a full explanation to this question, see:
https://magoosh.com/gmat/2014/compound-i ... -the-gmat/Mike

Variables in the question that are repeated in the answer choices? Let's Plug In!
Picking good numbers can make our lives easy. Let's make A=$1 and R=1 (100%). At the end of the first year, we have $2. At the end of the second year, we have $4. At the end of the third year, we have $8. Interest earned was $8-$1 = $7.
Let's check the answer choices:
(A) \(1(1)^3 = 1\) Nope.
(B) \(1(1 + 1^3) = 2\) Nope.
(C) \(1(3 + 3(1^2) + (1^3)) = 8\) Okayyyyy.
(D) \(3(1)^3 = 3\) Nope.
(E) \(3(1 + 1^2 + 1^3) = 9\) Nope.
Answer choice C.
ThatDudeKnowsPluggingIn