OG数学

brigittew

1.There are 4 card-processing machines in an office. The fastest of these machines processes x cards in 7 hours and the slowest processes x cards in 8 hours. Which of the following cound Not be the average time per machine for each of the 4 machines to process x cards?1)7.2  2)7.3  3)7.5  4)7.6  5)7.7
my answer is 7.25--7.75, so here we choose 1
2.if a taxi driver charges x cents for the first quarter-mile of a trip and x/5 cents for each additional quarter-mile, what is the charge, in cents, for a trip whose distance in miles is the whole number y? a.(x+sy)/125  b.( 4x+4xy)/5  c. (4x+xy)/500  d. (4x+xy)/5   e. xy/25
my method: x+(y-1/4)/(1/4)*(x/5)=b
3.In the figure above, two searchlights S1 and S2 are located 10,000 feet apart; each covers an area of radius 10,000 feet, and each is located 8,000 feet from the railroad track. To the nearest 1,000 feet, what is the total length x of track spanned by the searchlights? a. 24,000 b.22,000 c.20,000 d.16,000 e. 12,000
the figure as follows:
[upload=jpg]uploadImages/20029241617187443.jpg[/upload]

tongxun

1、同意你的答案。7778 ----7888
2、也同意。不过列式不一样：x+（y-1）*4（x/5）
3、B。从S1做一高至道路=8000，则三角型底边的1/2=6，000。S1S2=10，000，另一三角形的最外底边的1/2=6，000。所以总长=6000+6000+10000=22000。

brigittew

each covers an area of radius 10,000 feet, and each is located 8,000 feet from the railroad track. To the nearest 1,000 feet
按照你的解法，上述条件前2个构成了直角三角形，所以底边为6，000，可是to the nearest 1,000feet在这里什么意思？为什么跟它没有关系？

tongxun

我的算法中底边是12，000。我没用到“to the nearest 1,000feet”这个条件。
答案对吗？

brigittew

我看了，答案是对的