Hi mehaksal, this can be solved as follows -
Logic:
Communities without a couple = [Total Combinations (comunities)] - [combinations (communities) where a couple is together]
Total 3 member communities out of 10 people = 10C3 = 120
Combinations where couple is together = 5C1*8C1 = 5*8 = 40 (because 5C1 indicates selection of one couple which includes 2 people; the remaing person can be any one from the remaining 8 left after selection of the 2 persons married to each other)
Reqd = 120 - 40 = 80
Hope this clarifies
"Your time is limited, so don't waste it living someone else's life. Don't be trapped by dogma - which is living with the results of other people's thinking. Don't let the noise of others' opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition. They somehow already know what you truly want to become. Everything else is secondary" - Steve Jobs
