※ 引述《Diablotin (咕噜咕噜)》之铭言： : 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 : 恳求详细算法 感谢你 y miles 的速率为 x ，所费时间即为y/x 40-y miles的速率为1.25x，所费时间即为(40-y)/1.25x 目前Marla总费时 = y/x+(40-y)/1.25x 若以平均速率x的总费时为 40/x 题目要求的是ratio，所以就拿上面的公式除下面的公式， 二者相比就简化成 50/(0.25y+40) 可以发现x已经被约掉了，所以(1)没有用， (2)给了y=20，就可以算出答案… --

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