Problem 21 · 2021 Math Kangaroo
Stretch
Counting & Probability
careful-counting
3 girls and 2 boys were dancing. They danced in pairs so that each girl danced with each boy for exactly 1 minute. At any time, there was only one pair on the dance floor. For how many minutes did they dance?
Show answer
Answer: B — 6
Show hints
Hint 1 of 3
Only one pair dances at a time, so the total minutes equals the number of pairs.
Still stuck? Show hint 2 →
Hint 2 of 3
Each girl needs to dance once with each boy.
Still stuck? Show hint 3 →
Hint 3 of 3
Count all the different girl-and-boy pairs you can make.
Show solution
Approach: count the pairs
- There are 3 girls and 2 boys, giving 3 × 2 = 6 different pairs.
- Each pair dances for 1 minute, one pair at a time.
- So they dance for 6 minutes, option B.
Mark:
· log in to save