# 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* + 10*eh*

C. *eh* + 10*d*

D. *eh*(*d* – 10)

E. *h*(*d* + 10*e*)

**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.