Mathematics > Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

A machine can insert letters in envelopes at the rate of 120 per minute. Another machine can stamp the envelopes at the rate of 3 per second. How many such stamping machines are needed to keep up with 18 inserting machines of this kind?

(A) 12

(B) 16

(C) 20

(D) 22

(E) 24 

正确答案>>>