PP1-DS122

[purpleme]

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】B

詳解版上的答案我有點不懂

y*x+(40-y)*(1.25X)/x分之40=y+(40-y)*(1.25)/40

想問一下為什麼除x分之40阿?
等號後面又是怎麼求的呢
THX!

[purpleme]

有人會這題嗎.......
HELP~~~~~~~~

[larry.tw]

這題用網站表示很不好表示清楚(詳解我再補完整的)
題目是問: 全程如果用x mile所花的時間: 全程用題目的數據所花的時間

距離/速度=時間

y..........40-y
--- + --------
x ........1.25x
------------------ <==題目就再問這個,所以你發現到x會被消掉,主導權在y而已
......40
......----
.......x