涛涛Gwd-22-Q2:求助谢谢

dreadpower

Gwd-22-Q2:

In planning for a trip, Joan estimated both the distance of the trip, in miles, and her average speed, in miles per hour.  She accurately divided her estimated distance by her estimated average speed to obtain an estimate for the time, in hours, that the trip would take.  Was her estimate within 0.5 hour of the actual time that the trip took?

(1)      Joan’s estimate for the distance was within 5 miles of the actual distance.

(2)    Joan’s estimate for her average speed was within 10 miles per hour of her actual average speed.

Answer:e

请问Was her estimate within 0.5 hour of the actual time that the trip took?是什么意思？本题应该如何解？谢谢

mingzhu11

Was her estimate within 0.5 hour of the actual time that the trip took?

是说她估计的时间和实际时间是否在半个小时的误差内。

设actual distance为X，则estimated for the distance在 X+/-5范围内

设actual average speed为Y，则estimated average speed在Y+/-10范围内

 actual time ＝actual distance/actual average speed＝X/Y

estimated time=estimated distance/acestimated average speed=(X+/-5)/(Y+/-10)

显然estimated time—actual time可能不在0.5范围内