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June 2023 p52 q6
2837
In a group of 25 people there are 6 swimmers, 8 cyclists and 11 runners. Each person competes in only one of these sports. A team of 7 people is selected from these 25 people to take part in a competition.
Find the number of different ways in which the team of 7 can be selected if it consists of exactly 1 swimmer, at least 4 cyclists and at most 2 runners.
Solution
We need to find the number of ways to form a team of 7 people with exactly 1 swimmer, at least 4 cyclists, and at most 2 runners.
Consider the following scenarios:
1 swimmer, 4 cyclists, 2 runners: The number of ways to choose 1 swimmer from 6 is \(\binom{6}{1}\). The number of ways to choose 4 cyclists from 8 is \(\binom{8}{4}\). The number of ways to choose 2 runners from 11 is \(\binom{11}{2}\). Total for this scenario: \(\binom{6}{1} \times \binom{8}{4} \times \binom{11}{2} = 6 \times 70 \times 55 = 23100\).
1 swimmer, 5 cyclists, 1 runner: The number of ways to choose 1 swimmer from 6 is \(\binom{6}{1}\). The number of ways to choose 5 cyclists from 8 is \(\binom{8}{5}\). The number of ways to choose 1 runner from 11 is \(\binom{11}{1}\). Total for this scenario: \(\binom{6}{1} \times \binom{8}{5} \times \binom{11}{1} = 6 \times 56 \times 11 = 3696\).
1 swimmer, 6 cyclists, 0 runners: The number of ways to choose 1 swimmer from 6 is \(\binom{6}{1}\). The number of ways to choose 6 cyclists from 8 is \(\binom{8}{6}\). The number of ways to choose 0 runners from 11 is \(\binom{11}{0}\). Total for this scenario: \(\binom{6}{1} \times \binom{8}{6} \times \binom{11}{0} = 6 \times 28 \times 1 = 168\).
Adding these scenarios together gives the total number of ways: \(23100 + 3696 + 168 = 26964\).