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ajinkya bhole Grade: 10
        we wish to select 6 persons of 8,but if the person A is selected then B must be chosen. in how many ways can the selection be made?(plz explain)
7 years ago

Answers : (2)

Badiuddin askIITians.ismu Expert
147 Points

Dear ajinkya

case 1  :   A and B is not included

 then number of ways = 6C6 = 1


case 2 : B is selected A is not selected

 number of ways  = 1* 6C5  = 6


case 3:  A and B both are selected

 number of ways = 1*1* 6C4 = 15


so total ways  = 1+6+15 =22

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7 years ago
13 Points
i) When A is chosen: In this case we can chose the remaing 5 from 7 in 7C5 ways
​ii) When A is not chosen: In this case B is not chosen as well. So we now have to select all 6 from the remaining 6 (as A and B have been removed from the previous 8). This can be done in 6P6 ways.
Hence, the required number of ways = 7C6P6  = 7!/ 5! x 2! + 6!/ 6! x 0! = 7x6/2 + 6!/6! = 21+1 = 22
2 months ago
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