At a community fair, Mina and Amir decorated the rim of a circular food stall. The stall has a radius of 140 cm. The rim is made from identical round tiles and identical rectangular tiles, arranged so that their lengths fit exactly around the circle. Each round tile has a diameter of 16 cm, and each rectangular tile is 64 cm long. One round tile is followed by one rectangular tile, and this pair repeats all the way round. How many rectangular tiles were used around the rim? (Take π = 227.)
Need a hint?
Find the circumference of the stall first. Then find the combined length of one round tile and one rectangular tile.
Worked answer
- Circumference of the stall = 2 × 227 × 140 = 880 cm.
- Length of one repeating pair = 16 + 64 = 80 cm.
- Number of pairs = 880 ÷ 80 = 11.
- There is 1 rectangular tile in each pair, so 11 rectangular tiles were used.
The mistake this question tests
Stopped at one part in ratio
Dividing the circumference by the length of one round tile alone gives the wrong count. The repeating unit must include one round tile and one rectangular tile.
How to fix it at home →Wrong answers children often give:
- 22 Calculation slip
- 55 Stopped at one part in ratio
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