数学题目

taozike · 发表于 2009-12-31 16:59:19

A certain pilot flew 400 miles to City K at an average speed of 350 miles per hour with the wind and made the trip back at an average speed of 250 miles per hour against the wind. Which of the following is closest to the pilot’s average speed, in miles per hour, for the round-trip?
B

A. 280

B. 290

C. 300

D. 310

E. 320

设风的的速度是x, 那么

v=800/[400/ (350+x)+400 / (250-x)],

接下来怎么算我就不知道了，有谁知道，帮我解答一下。

a10285 · 发表于 2009-12-31 17:13:09

LZ想复杂了，350 miles per hour with the wind
250 miles per hour against the wind
这两个速度已经包含了风的速度
v=800/（400/ 350+400 / 250)=291. 6666≈290
选B

taozike · 发表于 2009-12-31 17:14:49

哦，这样呀，我高估了题目，谢谢，明白了

数学题目

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