A question paper has two parts, part A and part B, each containing 10 questions. If the student has to choose 8 from part A and 5 from part B, in how many ways can he choose the questions?
The question paper has two sets each containing 10 questions . so the student has to choose 8 from part A and 5 from part B.
⇒choosing 8 questions from 10 of part A in
10C8
⇒ choosing 5 questions from 10 of part B in
10C5
⇒by Multiplication principle, we get
=total no. of ways in which he can attempt the paper is
10C8
10C5
Applying nCr = 
1