Question

The number of ways of selecting $10$ books from book store containing unlimited number of Physics, Chemistry, Mathematics and biology books is

Answer 1

Let number of books of Physics, Chemistry, Mathematics and Biology be represented as $P,C,M,B$
$\therefore P+C+M+B=10$
So, number of solutions
$={}^{10+4-1}{C}_{4-1}={}^{13}{C}_3=286$