Permutation and Combination

Three children,each accompanied by a guardian,seek admission in a school.The principal wants to interview all the 6 persons one after the other,subject to the condition that no child is interviewed before its guardian.In how many ways can this be done?


1 Answers

Soumyadeep Basu ·

Total no. of ways without any restrictions is 6!=720.
For every child-guardian pair, there are two possibilities: either the child comes first or the guardian comes first. Now, discarding the cases where the child comes first for the three pairs, the total no. of ways is 7202.2.2=90.

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