A rectangular notice board has an area of 4800 cm² and a breadth of 60 cm. A total of 30 pins are placed around its edge, with one pin at each corner. The pins along each breadth are 12 cm apart. The pins along each length are also evenly spaced. What is the distance between two consecutive pins along the length of the board?
Need a hint?
Work out the length of the board first, then count how many gaps lie on the two breadth sides before sharing out the rest.
Worked answer
- Length of board = 4800 ÷ 60 = 80 cm.
- Each breadth side has 60 ÷ 12 = 5 gaps, so the two breadth sides have 2 × 5 = 10 gaps.
- The two length sides share the remaining 30 − 10 = 20 gaps, so each length side has 10 gaps.
- Distance along the length = 80 ÷ 10 = 8 cm.
The mistake this question tests
Area and perimeter formulas
Pupils often divide the 80 cm length by 20 gaps, forgetting that the two breadth sides already use 10 of the 30 gaps.
How to fix it at home →Wrong answers children often give:
- 4 Area and perimeter formulas
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