Question

大家帮我解答一下用英语出的数学题 thanks

1.How many committees of four can be formed from 20 Repiblicans and 15 Democrats if two members of each party must be the committee?

2.How many committees of four can be formed from 20 Repiblicans and 15 Democrats if at least one Republican and at least one Democrat must be on the committee?

3.A class consists of ten freshmen,twelve sophomores,and eight juniors.How many ways can five of these students be selected to serve on a committee?

4.A quality control inspector samples 4 computer chips from a box containing 10 computer chips.If the box contains 2 defective chips,in how many ways can he select a sample so that:
[a] all 4 are good?

[b]both defective chips are selected?

Answer 1

1.C(20,2)*C(15,2)=190*105=19950.
2.C(20,1)*C(15,3) + C(20,2)* C(15,2) + C(20,3)* C(15,1)=46150.
3.C(10+12+8,5)=142506.
4. a C(8,4) = 70
b.C(8,2) = 28

Answer 2

1.排列一下，C20(2)C15(2)
2.C20(1)C15(1)C33(2)
3.C30(5)C5(3)
4.C10(2)C8(4)
数学丢了好久了，也不确定对不对