以下問題,實在想不出來思考盲點,請各位高手幫忙解惑了~
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
做越多題,越來越沒信心了..
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