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 the excursion party be chosen?
Case 1: When all 3 joins.
Remaining 7 people are to be chosen from 25-3 = 22 people.
Number of ways = 22C7
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= 170544
Case 2:
When all 3 don’t join.
Remaining 10 people are to be chosen from 25-3 = 22 people.
Number of ways = 22C10
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= 646646
Total ways = 170544 + 646646
= 817190
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