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166.
17879-!-item-!-187;#058&011634 70, 75, 80, 85, 90, 105, 105, 130, 130, 130 The list shown consists of the times, in seconds, that it took each of 10 schoolchildren to run a distance of 400 meters. If the standard deviation of the 10 running times is 22.4 seconds, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?
(A) One (B) Two (C) Three (D) Four (E) Five
选B，看不懂，也不会做。。
3 A manufacturer produced x percent more video cameras in 1994 than in 1993 and y percent more video cameras in 1995 than in 1994. If the manufacturer produced 1,000 video cameras in 1993, how many video cameras did the manufacturer produce in 1995 ? 1 xy=20 2 X+Y+XY/100=9.2 答案选B 请问2为什么可以求出？
4. Working alone at its own constant rate, a machine seals k cartons in 8 hours, and working alone at its own constant rate, a second machine seals k cartons in 4 hours. If the two machines, each working at its own constant rate and for the same period of time, together sealed a certain number of cartons, what percent of the cartons were sealed by the machine working at the faster rate?
(A) 25%
(B)
(C) 50%
(D) 66*2/3%
(E) 75% 选D， 看不懂题目也不会解答
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发表于 2008-9-22 21:05:00
1+X/100)(1+Y/100)=1+x/100+y/100+xy/10000
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