Question

From a class of 25 students, 10 are to be chosen for an excursion party.
There are 3 students who decide that either all of them will join or none
of them will join. In how many ways can they be chosen?

Answer 1

From the class of 25 students, 10 are to be chosen for an excursion party.

Case I: All the three students join.Then, the remaining 7 students can be chosen from the remaining 22 students in ways.

Case II: None of the three students join.Then, 10 students can be chosen from the remaining 22 students in ways.

Thus, required number of ways of choosing the excursion party is