Answer : Since there are 10 different books out of which 4 is to be selected .
- When there is no restriction
No. of ways in which 4 books be selected = 10C4
= 210 ways
- Two particular books are always selected
Since two particular books are always selected, so ways of selecting 2 books from 8 are
= 8C2 ways
= 28 ways
- Two particular books are never selected
Since two particular books are never selected so, ways of selecting 4 books from 8 are
= 8C4 ways
= 70 ways