请教3道Prep数学题

Beaconhill

Of the students who eat in a certain cafeteria, each student either likes or dislikes lima beans and each student either likes or dislikes brussels sprouts. Of these student, 2/3 dislike lima bean, and of those who dislike lima beans, 3/5 also dislike brussels sprout. How many of the students like brussels sprouts but dislike lima beans?

(1) 120 students eat in the cafeteria

(2) 40 of students like lima beans.

ans-D. 我怎么求不出来？喜欢lima beans里的人有多少喜欢brussel sprouts的没给呀？

If $1,000 is deposited in a certain bank account and remains in the account along with any accumulated interest, the dollar amount of interest, I, earned by the deposite in the first n years is given by the formula I=1,000 [(1+r/100)n-1],where r percent is the annual interest rate paid by the bank. Is the annual interest rate paid by the bank greater than 8%?

(1) the deposit earns a total of $ 210 in interest in the first 2 years.

(2) (1＋r/100)2>1.15 

(2是平方）（n也是次方）

答案是A，为什么不是D？第2个不是也可以求出r吗？

The number of 75 can be written as the sum of the squres of 3 different positive integers. what is the sum of these 3 intergers?

13

我是凑出来的，有规律的求法吗？

谢谢

allln123123

1.either likes or dislikes 比较重要啊

(1) 120 students eat in the cafeteria+2/3 dislike lima bean, and of those who dislike lima beans, 3/5 also dislike brussels sprout

可以得出 40 like lb,80 dislike lb,其中又有30 dislike bs,50 like bs

(2)可以依次类推

2.(2)只能推出r>7%,真到考试的时候还比较难办

3.没什么太好办法,75=a^2+b^2+c^2,假设a=b=c,可以得出他们等于5,那么其中一个就是5,其余的再从1-4是

Beaconhill

哦，谢谢。。第一题没看清问题。

第三题a=b=c的假设是怎么来的？

allln123123

没有拉 ,只是这样好凑一点 因为75=3*25=5^2+5^2+5^2