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We wish to select 6 persons from 8, but if the person A is chosen, thenB must be chosen. In how many ways can the selections be made?A. 20B. 21C. 22D. 30 |
Answer» Correct Answer - C Total number of person = 8 Number of person to be selected = 6 It is given that, if A is chosen then, B must be chosen. Therefore, following cases arise. Case I When A is chosen, B must be chosen. Number of ways `= ""^(8 -2)C_(6-2) = ""^(6)C_(4)` Case II When A is not chosen. `therefore" "` Number of ways `= ""^(8 -1)C_(6) = ""^(7)C_(6)` Hence, required number of ways `= ""^(6)C_(4) + ""^(7)C_(6)` `= 15 + 7 = 22` |
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