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SAT I 一日一问：2013年8月12日
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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 pens priced at dollars each and pens priced at dollars each, which of the following expresses, in terms of and , the average (arithmetic mean) price, in dollars, of these pens? 

(A) (3 times t) + (3 times u) over (t + u)
(B) (3 times t) + (3 times u) over (t imes u)
(C) (3 times t times u) over (t + u)
(D) ((2 times t) + (4 times u)) over (t + u)
(E) ((2 times t) + (4 times u)) over (t times u)

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The correct answer is D

Explanation

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 2 times t dollars. There are u pens priced at 4 dollars each, so the total price of these pens is 4 times u dollars. Thus the total price of all of the pens is (2 times t) + (4 times u)dollars, and the total number of pens is t + u, the average price, in dollars, of all of these pens is ((2 times t) + (4 times u)) over (t + u).