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Difficulty: 4/102024 NMTC 2024 (QII-38)

From group 7 men and 6 women, five persons are to be selected to form committee so that at least 3 men are there in the committee. In how many ways can it be done?

Guide / Hint

Hint 1: Break the problem down into three disjoint cases based on the number of men: exactly 3, 4, or 5 men.

Hint 2: Use the combination formula to find the number of ways for each case.

Hint 3: Multiply the choices of men and women within each case, and add the three case results together.

Solution

Step 1 (Identify Cases): We need to choose a 5-person committee from 7 men and 6 women such that there are at least 3 men in the committee. The possible structures for the committee are:

  • Case 1: Exactly 3 men and 2 women

  • Case 2: Exactly 4 men and 1 woman

  • Case 3: Exactly 5 men and 0 women

Step 2 (Calculate Combinations for each case):

  • Case 1 (3 Men, 2 Women): Choose 3 men from 7 and 2 women from 6:

  • Case 2 (4 Men, 1 Woman): Choose 4 men from 7 and 1 woman from 6:

  • Case 3 (5 Men, 0 Women): Choose 5 men from 7:

Step 3 (Sum the Cases): Total ways = .

Step 4 (Conclusion): There are exactly 756 distinct ways to form the committee.

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    2024 NMTC 2024 QII-38 - Olympiad Math Olympiad Question | Leminno