Out of 100 students two sections of 40 and 60 students are formed. If you and your friends are among the 100 students, what is the probability that i.                You both enter the same section? ii.              You both enter the different section?

Explanation

My friend and I are among the 100 students

Total number of ways of selecting 2 students out of 100 students =`.^100C_2`
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(a) The two of us will enter the same section if both of us are among 40 students or among 60 students


∴ Number of ways in which both of us enter the same
section = `^40C_2​+(^60C_2)`
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∴ Probability that both of us enter the same section
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