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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+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) (4x)+12
(B) (4x)+24
(C) (6x)+30
(D) (8x)+24
(E) (8x)+36

答案和解析

答案：D

解析：

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