Ariel's toy railway track has a curved section made from 2 identical large semicircular pieces and 2 identical small semicircular pieces. Each small piece has radius 5 cm, and the total length of all 4 curved pieces is 87.92 cm. Find the radius of each large piece. (Take π = 3.14)
- 9 cm
- 14 cm
- 19 cm
- 23 cm
Need a hint?
Find the total curved length of one large-and-one-small pair first.
Worked answer
- The curved length of a semicircle is π × its radius.
- Let R be the radius of each large semicircular piece.
- 2 × 3.14 × (R + 5) = 87.92.
- R + 5 = 14.
- R = 9 cm.
Answer: 9 cm
The mistake this question tests
Habit
Radius and diameter in circles
Some pupils count only one large piece and one small piece, so the calculated radius is too large.
How to fix it at home →Wrong answers children often give:
- 23 cm Radius and diameter in circles
- 14 cm Calculation slip
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