A medium question on tree planting for P3–P4, with a step-by-step solution, diagrams and the answer. Common in the Hua Xia Cup's P2 to P5 papers. Sawing logs, striking clocks and lining up lamp posts are all the same problem.
The question
A round pond in the park is 40 m around its edge.
A gardener plants a ring of trees along the edge, with neighbouring trees 4 m apart.
Then, between every two neighbouring trees, he puts 2 pots of flowers.
How many pots of flowers does he put out?
Show the hints (2)
💡Hint 1: Round a circle, is there a gap between the last tree and the first?
💡Hint 2: First count the gaps round the circle — each gap is one 'between two neighbouring trees'.
Worked solution
Have a go first, then read the solution step by step.
1.The ring splits into 40 ÷ 4 = 10 gaps. Round a circle the ends join, so there are 10 trees too — nothing to add or take away.
2.2 pots per gap: 10 × 2 = 20 pots.
⚠️Common mistake: counting only 9 gaps (18 pots) and missing the gap between the last tree and the first.
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