Hello Bijay,
This is a question where you can use the reverse engineering approach of solving combinations questions. Not sure what I’m telling? Remember that in one of my sessions on Combinatorics, I had given out a principle,
What I want = Total – What I don’t want.
So, what do we not want here?
We do not want the team to have a couple.
IN how many ways can a couple be a part of a team?? We need a TEAM OF 3 persons. Of these 3 persons, if we have ONE COUPLE, we already have 2 persons, isn’t it? How many MORE will we have to select? We will need one more person, apart from the couple we selected.
We have 5 couples, so selecting ANY ONE of them can be done in \(5_C_1\) ways.
Once this is done, we will be left with 8 persons. Of the 8 persons, we need to select ANY ONE; this can be done in \(8_C_1\) ways,.
Therefore, the number of ways of selecting a team of 3 persons which HAS ONE COUPLE = \(5_C_1\) * \(8_C_1\) = 5 * 8 = 40.
Do we want the above 40? No, we don’t. Therefore, we subtract this from the TOTAL number of 3-member teams that can be formed.
Total number of 3-member teams that can be formed = \(10_C_3\) = 120.
Therefore, Number of 3-member teams WITHOUT a couple = 120 – 40 = 80.
The correct answer option is B, IMO.
Hope that helps!