CAT 2022 Slot 1 QA Question & Solution

Modern MathHard

Question

The number of ways of distributing 20 identical balloons among 4 children such that each child gets some balloons but no child gets an odd number of balloons, is

Solution

Let the number of balloons each child received be 2a, 2b, 2c and 2d

2a + 2b + 2c + 2d = 20

a + b + c + d = 10

Each of them should get more than zero balloons.

Therefore, total number of ways = $(n-1)_{C_{r-1}}=(10-1)_{C_{4-1}}=9_{C_3}=84$