请教费费逻辑与数学(绿皮)

Sarah006

Of the science books in a certain supply room,50 are on botany,65 are on zoology ,90 are on physics,50 are on geology,and 110 are on chemistry.If science books are removed randomly from the supplyroom,how many must be removed to ensure that 80 of the booksremoved are on the same science ?

我对这个题目的意思不大明白,不知道如何下手,请教一下大家哦

谢谢

hitlzc

总共有50+65+90+50+110=365本书

how many must be removed to ensure that 80 of the booksremoved are on the same science ?

因为每本书是随机移出的，所以移出的概率一样

因此数量最多的chemistry移出的概率最大110/365。

设X为需移出的最小数。

有110/365=80/x

x=265.45

取266

 

Sarah006

可是答案是324阿？？

hitlzc

哦，抱歉，是我理解错了MUST的意思。

因为大于80本的只有90和110。

MUST就是要求数量少的90本也能保证，所以应为

90/365=80/X

X=324

熏依草

狒狒上课这样讲的,这是道保证题,先不保证,即先不满足条件取就是这样,50+65+79+50+79

再保证,就是50+65+79+50+79+1=324,嘿嘿