Re: [問題] GWD22-Q19

看板GMAT (GMAT入學考試)作者chilis (chilis)時間17年前 (2008/11/11 17:28)推噓1(1推 0噓 0→)

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※ 引述《yyiitt1003 (懷念補習班的日子)》之銘言： : 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 這題w根本是擾亂你的把w看成全部的進度,當成100%即可量= T*S, S=量/T假設X花d+2天完成w，Y花d天完成w X的產率w/(d+2), Y的產率w/d, 一起工作3天產生出5w/4, [ w/(d+2) + w/d ]=5w/4除以3, 12/d+12/(d+2)=5d(d+2) 得~ 12d+24+12d=5d^2+10d , 5d^2-14d-24=0 (5d+6)(d-4)=0, d= -6/5,4~ X產W需要4+2=6天題目問2W,所以2*6=12 天~ 選(E) : 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.. 選3輛，可以重複選，所以分母就是3*3*3，分子(3*2*1)是這樣的，第一次可以隨便選，第二次是剩下的2個選1個，最後一次就是最後剩下的那輛， 3*2*1/3^3= 2/9 選(C) -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 210.244.13.211