以下问题,实在想不出来思考盲点,请各位高手帮忙解惑了~ Running at their respective constant rates, macgine X takes 2 days longer to produce w widgets than machine Y.At these rates,if the machines together produce 5/4w widgets in 3 days,how many days would it take machine X alone to produce 2w widgets? Ans.12 A certain roller coaster has 3 cars,and a passenger is equally likely to ride in any 1 of the 3 cars each time that passenger rides the roller coaster. IF a certain passenger is to ride the roller coaster 3 times, what is the probability that the passenger will ride in each of the 3 cars? Ans. 2/9 There are 8 books on a shelf,of which 2 are paperbacks and 6 are hardbacks.How many possible selections of 4 books from this shelf include at least one paperback? Ans. 50 做越多题,越来越没信心了.. --

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