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.

1. What was the distance from the top of the 1st oval ring to the bottom of the 4th oval ring?
2. The distance from the top of the 1st ring to the bottom of the last ring was 265 cm. How many oval rings did Rachel hang altogether?

(a)
Distance of 1 oval ring = 13 cm = 1 x 12 + 1
Distance of 2 oval rings = 25 cm = 2 x 12 + 1
Distance of 3 oval rings = 37 cm = 3 x 12 + 1

Distance from the top of the 1st oval ring to the bottom of the 4th 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 12 + 1

Number of oval rings x 12 + 1 = 265
Number of oval rings x 12 = 265 - 1
Number of oval rings x 12 = 264
Number of oval rings = 264 ÷ 12
Number of oval rings = 22

Number of oval rings that Rachel hung altogether = 22

Answer(s): (a) 37 cm; (b) 22