Question: The number of ways of distributing 8 identical balls in 3 distinct boxes so that none of the boxes is empty is
Options:
A)  $ ^{8}C_3 $
B) 21
C)  $ 3^{8} $
D) 5
  Show Answer
  Answer:
Correct Answer: B
Solution:
- [b] Required number of ways = coefficient of  $ x^{8} $  in  $ {{(x+x^{2}+..x^{6})}^{3}} $  [ $ \because  $  Each box can receive minimum 1 and maximum 6 balls] = coeff of  $ x^{8} $  in         $ x^{2}{{(1+x+x^{2}+…+x^{5})}^{3}} $  = coeff of  $ x^{5} $  in  $ {{( \frac{1-x^{6}}{1-x} )}^{3}} $  = coeff of  $ x^{5} $  in  $ {{(1-x)}^{-3}} $  = coeff of  $ x^{5} $  in  $ (1{{+}^{3}}C_1x{{+}^{4}}C_2x^{2}+…) $   $ {{=}^{7}}C_5=21 $