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Question
Five students are selected from 11. How many ways can these students be selected if two specified students are selected?
Solution
5 students are to be selected from 11 students
When 2 specified students are included then remaining 3 students can be selected from (11 – 2) = 9 students.
∴ Number of ways of selecting 3 students from 9 students = 9C3
= `(9!)/(3! xx 6!)`
= `(9 xx 8 xx 7 xx 6!)/(3 xx 2 xx 1 xx 6!)`
= 84
∴ Selection of students is done in 84 ways when 2 specified students are included.
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