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We wish to select 6 person from 8 but, if the person $A$ is chosen, then $B$ must be chosen. In how many ways can selections be made?
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Since total number of person $=8$
number of person to be selected $=8$
so it is a given that, if $A$ is choosen then $\mathrm{B}$ must be chosen Therefore, following two cases arise
Case 1: When $A$ is choosen $B$ must be chosen.
$\therefore$ Number of ways $={ }^{8-2} C_{6-2}={ }^6 C_4$
Case 2: When $A$ is not chosen.
Then, $B$ may be chosen,
$\therefore$ Number of ways $={ }^{8-1} \mathrm{C}_6={ }^7 \mathrm{C}_6$
Hence, required number of ways $={ }^6 \mathrm{C}_4+{ }^7 \mathrm{C}_6=15+7=22$
number of person to be selected $=8$
so it is a given that, if $A$ is choosen then $\mathrm{B}$ must be chosen Therefore, following two cases arise
Case 1: When $A$ is choosen $B$ must be chosen.
$\therefore$ Number of ways $={ }^{8-2} C_{6-2}={ }^6 C_4$
Case 2: When $A$ is not chosen.
Then, $B$ may be chosen,
$\therefore$ Number of ways $={ }^{8-1} \mathrm{C}_6={ }^7 \mathrm{C}_6$
Hence, required number of ways $={ }^6 \mathrm{C}_4+{ }^7 \mathrm{C}_6=15+7=22$
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