推 Diablotin:感謝感謝！ 08/22 14:29
※ 引述《Diablotin (咕嚕咕嚕)》之銘言：
: 122. 12343-!-item-!-187;#058&008383
: During a 40-mile trip, Marla traveled at an average speed of x miles per hour
: for the first y miles of the trip and at an average speed of 1.25x miles per
: hour for the last 40 - y miles of the trip. The time that Marla took to
: travel the 40 miles was what percent of the time it would have taken her if
: she had traveled at an average speed of x miles per hour for the entire trip?
: (1) x = 48
: (2) y = 20
: 答案是B
: 懇求詳細算法 感謝你
y miles 的速率為 x ，所費時間即為y/x
40-y miles的速率為1.25x，所費時間即為(40-y)/1.25x
目前Marla總費時 = y/x+(40-y)/1.25x
若以平均速率x的總費時為 40/x
題目要求的是ratio，所以就拿上面的公式除下面的公式，
二者相比就簡化成 50/(0.25y+40)
可以發現x已經被約掉了，所以(1)沒有用，
(2)給了y=20，就可以算出答案…
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※ 編輯: winandos 來自: 118.168.243.194 (08/21 17:09)