10. A community of 3 people is to be selected from 5 married couples, such that the community does not include two people who are married to each other. How many such communities are possible?
(d) 80
Sol: No. of ways to pick 3 individuals out of 5 couples such that a couple is included is 5C1*8C1 = 5*8 = 40
(Order of choice here doesn’t matter)
Total no. of ways to pick 3 people from ten = 10C3 = 10*9*8/(3*2) = 120
Therefore ways to select 3 individuals out of 5 couples such that no couple is included = 120-40 = 80.