PSLE Lucy hung some identical oval rings vertically. The thickness of each oval ring was 1 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 4th oval ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 200 cm. How many oval rings did Lucy hang altogether?
(a)
Distance of 1 oval ring = 11 cm = 1 x 9 + 2
Distance of 2 oval rings = 20 cm = 2 x 9 + 2
Distance of 3 oval rings = 29 cm = 3 x 9 + 2
Distance from the top of the 1st oval ring to the bottom of the 4th oval ring = 29 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 9 + 2
Number of oval rings x 9 + 2 = 200
Number of oval rings x 9 = 200 - 2
Number of oval rings x 9 = 198
Number of oval rings = 198 ÷ 9
Number of oval rings = 22
Number of oval rings that Lucy hung altogether = 22
Answer(s): (a) 29 cm; (b) 22