Permutation and Combination

21 books of English and 19 books of Hindi can be arrranged in such a way that 2 Hindi books wont come together ??
Question by Harsh Bodgal
<Answer by Alltricks>
21 -E
19 -H

NO --HH
_E_E_E_E_E_E_E_E_E_E_E_E_E_E_E_E_E_E_E_E_E_
22 places where H can be placed

22C19
=nCr=nC(n-r)=22C3
nCr = n! / r! * (n - r)!
=22!/19!*3!
=22*21*20*19! / 3!*19!
=22*21*20/3
=22*7*20
=3080