[求助]弱弱问两道数学题。。。

1、  A certain club has 20 members. What is the ratio of the member of 5-member committees that can be formed from the members of the club to the member of 4-member committees that can be formed from the members of the club?

答案：16 to 5

2、What is the greatest prime factor of 2¹⁰⁰-2⁹⁶?    

答案： 5

谢谢各位了~~~~~~

1.C(5,20)/C(4,20)=16/5

2.2^100-2^96=2^96(2^4-1)=2^96*15=2^96*3*5,so the greatest prime factor is 5

明白了。。谢谢~~