Mathematics > Standard Multiple Choice

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

Machine X, working at a constant rate, can produce x bolts per hour. Machine Y, working at a constant rate, can produce x plus 6 bolts per hour. In terms of x, how many bolts can both machines working together at their respective rates produce in 4 hours?

(A) (4 x) +12

(B) (4 x) +24

(C) (6 x) +30

(D) (8 x) +24

(E) (8 x) +36 

正确答案>>>

The correct answer is D

Explanation

Machine X, working at a constant rate, can produce x bolts per hour, and machine Y, working at a constant rate, can produce x plus 6 bolts per hour. Therefore, in one hour, both machines working together at their respective rates can produce x plus x plus 6 equals (2 x) +6 bolts. It follows that in 4 hours, both machines working together at their respective rates can produce 4 ((2x) +6) equals (8 x) +24 bolts.