这四道题是新东方的模考题十的，望好心的同学帮我解答一下，数学菜鸟就此谢过！ 1.Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y. At these days, if the two machines together produce 5/4 w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets? A 4 B 6 C 8 D10 E12
2.For any positive integer n, the sum of the first n positive integers equals [n(n+1)]/2, what is the sum of all the even integers between 99 and 301? A 10100 B 20200 C 22650 D 40200 E 45150
3, A gardener is going to plant 2 red rosebushes and 2 white rosebushes. If the gardener is to select each of the bushes at random, one at a time, and plant them in a row, what is the probability that the 2 rosebushes in the middle of the row will be red rosebushes? A 1/12 B1/6 C 1/5 D 1/3 E 1/2
4.If n is the product of the integers from 1 to 20 inclusive, what is the greatest integer k for which 2k is a factor of n? A 10 B 12 C 15 D 18 E 20
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发表于 2010-9-19 19:48:57
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