PSLE Rachel 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 5th oval ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 110 cm. How many oval rings did Rachel hang altogether?
(a)
Distance of 1 oval ring = 14 cm = 1 x 12 + 2
Distance of 2 oval rings = 26 cm = 2 x 12 + 2
Distance of 3 oval rings = 38 cm = 3 x 12 + 2
Distance from the top of the 1st oval ring to the bottom of the 5th oval ring = 38 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 12 + 2
Number of oval rings x 12 + 2 = 110
Number of oval rings x 12 = 110 - 2
Number of oval rings x 12 = 108
Number of oval rings = 108 ÷ 12
Number of oval rings = 9
Number of oval rings that Rachel hung altogether = 9
Answer(s): (a) 38 cm; (b) 9