A certain business produced x rakes each month form November through February and shipped x/2 rakes at the beginning of each month from March through October. The business paid no storage costs for the rakes from November through February, but it paid storage costs of $0.10 per rake each month from March through October for the rakes that had not been shipped. In terms of x, what was the total storage cost, in dollars, that the business paid for the rakes for the 12 months form November through October?

A. 0.40x

B. 1.20x

C. 1.40x

D. 1.60x

E. 3.20x

Answer: c,why

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Q17:

A driver completed the first 20 miles of a 40-mile trip at an average speed of 50 miles per hour. At what average speed must the driver complete the remaining 20 miles to achieve an average speed of 60 miles per hour for the entire 40-mile trip? (Assume that the driver did not make any stops during the 40-mile trip.)

A. 65 mph

B. 68 mph

C. 70 mph

D. 75 mph

E. 80 mph

Answer: d ,why not c

11. 11月-2月每月生产x，一共4x

从3月到10月每月月初运走x/2。从3月开始，每个月要为每个rake花1毛钱保管费。问总保管费

3月花了3.5*0.1=0.35x，4月花了0.3x……每月比上月少花0.05x

等差数列，从0.35x加到0.05x

0.35+0.3+0.25+0.2+0.15+0.1+0.05=1.4

17

一共40mile，前一半速度50迈，要想达到平均速度60迈，后一半需要开多少？

设后一半需要开x迈

前20花了20/50=0.4小时。总路程40，除以总时间0.4+20/x=60

0.4+20/x=2/3

20/x=4/15

x=75