An easy question on tree planting for P2–P3, 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 carpenter is sawing a long plank into 4 pieces.
He makes one cut at a time, and each cut takes 2 minutes.
How many minutes does he take altogether?
Show the hints (2)
💡Hint 1: One cut makes how many pieces? Two cuts?
💡Hint 2: First work out how many cuts give 4 pieces.
Worked solution
Have a go first, then read the solution step by step.
1.Each cut adds one piece: 1 cut gives 2 pieces, so 4 pieces need 4 − 1 = 3 cuts.
2.2 minutes a cut: 3 × 2 = 6 minutes.
⚠️Common mistake: 4 × 2 = 8, as if there were as many cuts as pieces.
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