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10 people are there and three need to chosen = 10C3 = 120
Out of these combinations there are also combination with a couple on group of three members. We need to subtract these from 120.
So no of ways in which one couple is in group is 1 * 8C1 = 8 and there are such 5 couple so we have 5*8 = 40 combinations
Hence total combinations = 120-40 = 80
Q2: There are 3+4+2 = 9 flags These can be arranged in 9! ways But there are 3 similar red flags, 4 similar yellow and 2 similar blue flags
So total combinations = 9!/( 3! * 4! * 2! ) = 1260