A team of is to be chosen from boys and girls. In how many ways can the team be chosen if it must contain exactly boys and girls?
Answer and explanation
Correct answer: C.
- Step 1: The boys can be chosen in ways and the girls in ways. Step 2. Each choice of boys goes with each choice of girls, so the number is . **Answer: . Why not the others:** is , which ignores the condition on boys and girls, adds the two counts instead of multiplying them, and counts ordered choices within each group.
Practise more Binomial expansion, permutations and combinations.
Free questions with an explanation for every one, and full timed Singapore GCE O-Level mock tests.