Question

A boy has 3 library tickets and 8 books of his interest in the library. Of these 8, he does not want to borrow Chemistry part II, unless Chemistry Part I is also borrowed. In how many ways can be choose the three books to be borrowed?

Answer 1

1) When chemistry part I is borrowed`=.^7C_2`
2) When chemistry part I is not borrowed`=.^6C_3`
Total number of ways`=.^7C_2+.^6C_3`
`=(7*6*3)/2+(6*5*4)/6`
`=21+20=41`.