请教一道Prep 数学题，急，谢谢啦

Jasmine0302 · 发表于 2010-6-7 17:25:10

A certain car averages 25 miles per gallon of gasoline when driven in
the city and 40 miles per gallon when driven on the highway. According
to these rates, which of the following is closet to the number of miles
per gallon that the car averages when it is drive 10 miles in the city
and then 50 miles on the highway.

A. 28
B. 30
C.33
D.36
E. 38

我觉得按比例算的话是25*10/(10+50) +40*50/(10+50) =37.5,所以选了E，最接近，但是答案是(D)36, 不知道是怎么算的，请大家帮帮忙看看吧

童XP · 发表于 2010-6-7 17:51:10

LZ用的是加权平均数，看OGreview一般average指的是arithmetic mean，所以个人认为这个题应该是（10+50）/(10/25+50/40)

Jasmine0302 · 发表于 2010-6-7 18:05:09

原来如此，多谢啦~

请教一道Prep 数学题，急，谢谢啦

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