[問題]GWD18-14

[balanana]

Q14:
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?

A. 280
B. 290
C. 300
D. 310
E. 320

Ans:B

我知道順風時,速度=350+風速,逆風時,速度=250-風速,
共行400*2=800miles
距離/時間=速度
請問接下來該怎麼算阿??
謝謝~

[kwtluck]

(800)/(400/350+400/250)=(800)/(96/35)=291.~約290

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