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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 the excursion party be chosen?
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Solution
Out of 25 students, 10 students are to be included in the tour group. But 3 out of 10 students are like this
(i) When all three join the touring party or
(ii) All three do not happen.
(i) Methods of selecting the excursion group when three students join the team = 22C7
(ii) Methods of selection when all three students are not included in the tour group = 22C10
Methods of selecting the touring party in both the cases = 22C7 + 22C10
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