[計量] pp ds 122 麻煩大家
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
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【答案】B
【思路】
Y*X+(40-Y)*(1.25)
___________________
40
_______
X
(1) Y是未知數,insufficient
(2) X被消除了, y = 20, sufficient
題目應該是在問，兩種方式所耗的時間的百分比，下面的40/x ，我可以理解
但是上面的Y*X +(40-Y)(1.25) ，我就搞不懂為什麼這樣列式了
請問板上眾高手，還有其他的思考方式或是列式嗎? 又或者是我沒有理解題目的意思?
以上，麻煩大家。
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