Question

Ron finds 9 books at a bookstore that he would like to buy, but he can afford only 5 of them. In how many ways can he make his selection? How many ways can he make his selection if he decides that one of the books is a must?
a. 3024; 1680
b. 7560; 840
c. 120; 1680
d. 126; 70

Answer 1

Answer:

d. 126; 70

Step-by-step explanation:

given that Ron  finds 9 books at a bookstore that he would like to buy, but he can afford only 5 of them.

Out of 9 books he has to select 5 of them

Here selection of books can be done in any order.  Hence order does not matter

No of ways he selects 5 books out of 9 books = 9C5

= 126

Part II

One book is a must

Hence he has options only 4 books from the remaining 8.

No of ways when one book is compulsory = selecting 3 books from 8 books

= 8C4

= 70

Option d is right.