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Mathematics>Standard Multiple Choice

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

If Kelly buys t pens priced at 2 dollars each and u pens priced at 4 dollars each, which of the following expresses, in terms of t and u, the average (arithmetic mean) price, in dollars, of these pens?

(A) (3t) + (3u)/(t+u)
(B) (3t) + (3u)/(tu)
(C) (3tu)/(t+u)
(D) ((2t) + (4u))/(t+u)
(E) ((2t) + (4u))/(tu)

答案和解析

答案：D

解析：

The average price of the pens is equal to the total price of all of the pens divided by the total number of pens. There are t pens priced at 2 dollars each, so the total price of these pens is 2t dollars. There are u pens priced at 4 dollars each, so the total price of these pens is 4u dollars. Thus the total price of all of the pens is (2t)+(4u) dollars, and the total number of pens is t+u, the average price, in dollars, of all of these pens is ((2t)+(4u))/(t+u).