SAT Math Multiple Choice Practice Question 571: Answer and Explanation

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Question: 571

7. A monthly Internet service costs d dollars for the first 10 hours, and e dollars per hour for each hour after the first 10. Which of the following could represent the cost of the service, if h represents the total number of hours the service was used this month?

A. d + e(h – 10)
B. d + 10eh
C. eh + 10d
D. eh(d – 10)
E. h(d + 10e)

Correct Answer: A

Explanation:

A This is a great Plugging In question. Make d = 2, so the first 10 hours cost $2.00, and e = 3, so service costs $3.00 an hour. Pick a number above 10 for h to make your math easier: If h = 20, it can be split into two parts: The first 10 hours cost $2.00, and the second 10 hours cost 10 × $3.00 = $30.00. Altogether that's $32.00, the number we're looking for in the answers. Plug in the values for d, e, and h. The expression in A becomes 2 + 3(20 – 10) = 2 + 3(10) = 32. A works, but always check all the answers just in case: B gives 602, C gives 80, D gives –480, and E gives 640. A is correct.

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