评论
打印
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).
