In how many ways can 5 books be selected from 12 books, with 2 particular books always left out?

Question: In how many ways can 5 books be selected from 12 books, with 2 particular books always left out?

Solution:
মোট বস্তু, n = 12
সর্বদা বাদ বা বর্জন থাকবে, m = 2
এবং প্রতিবার নিতে হবে, r = 5

∴ সমাবেশ = ^{(n - m)}C_r = ^{(12 - 2)}C₅
= ¹⁰C₅
= 10!/[5!(10 - 5)!]
= (10 × 9 × 8 × 7 × 6)/(5 × 4 × 3 × 2 × 1)
= 252