At a class party, each student randomly selects a wrapped prize from a bag. The prizes include books and calculators. There are 27 prizes in the bag. Meghan is the first to choose a prize. If the probability of Meghan choosing a book for her prize is $\frac{2}{3}$, how many books are in the bag?
(A) 15
(B) 9
(C) 21
(D) 7
(E) 18
Since Meghan chooses a prize from 27 in the bag and the probability of her choosing a book is $\frac{2}{3}$, then $\frac{2}{3}$ of the prizes in the bag must be books.

Therefore, the number of books in the bag is $\frac{2}{3} \times 27=18$.

ANSWER: (E)