We wish to select 6 persons from 8, but if the person A is chosen, then B must be chosen. In how many ways can the selection be made?
Question:
We wish to select 6 persons from 8, but if the person A is chosen, then B must be chosen. In how many ways can the selection be made?
Solution:
6 people are to be selected from 8.
There are two case.
(i) When A is selected, then B must be chosen.
$\therefore$ Number of ways $={ }^{6} C_{4}=15$
(ii) When A is not chosen:
Number of ways $={ }^{7} C_{6}=7$
∴ Total number of ways = 15 + 7 = 22