On Arun's town map, 3 cm represents 15 km. How many centimetres on the map represent 45 km?
Need a hint?
Compare the actual distance 45 km with 15 km first. The map distance must increase by the same factor.
Worked answer
- 45 ÷ 15 = 3, so the map distance is 3 times as large.
- 3 × 3 = 9 cm.
Answer: 9 cm
The mistake this question tests
Habit
Stopped at one part in ratio
Multiplying 45 by 3 gives 135, but 3 cm already represents 15 km, so the scale factor must be found first.
How to fix it at home →Wrong answers children often give:
- 15 Stopped at one part in ratio
- 135 Calculation slip
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See the answer →Practise PSLE ratio until the mistakes stop.
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