PSLE Fiona hung some identical oval rings vertically. The thickness of each oval ring was 2 cm. The figure shows how the oval rings are connected.
- What was the distance from the top of the 1st oval ring to the bottom of the 5th oval ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 224 cm. How many oval rings did Fiona hang altogether?
(a)
Distance of 1 oval ring = 15 cm = 1 x 11 + 4
Distance of 2 oval rings = 26 cm = 2 x 11 + 4
Distance of 3 oval rings = 37 cm = 3 x 11 + 4
Distance from the top of the 1st oval ring to the bottom of the 5th oval ring = 37 cm
(b)
Formula
Distance from the top of the 1st oval ring to the bottom of the last oval ring = Number of oval rings x 11 + 4
Number of oval rings x 11 + 4 = 224
Number of oval rings x 11 = 224 - 4
Number of oval rings x 11 = 220
Number of oval rings = 220 ÷ 11
Number of oval rings = 20
Number of oval rings that Fiona hung altogether = 20
Answer(s): (a) 37 cm; (b) 20