PSLE Wendy 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 6th oval ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 280 cm. How many oval rings did Wendy hang altogether?
(a)
Distance of 1 oval ring = 16 cm = 1 x 12 + 4
Distance of 2 oval rings = 28 cm = 2 x 12 + 4
Distance of 3 oval rings = 40 cm = 3 x 12 + 4
Distance from the top of the 1st oval ring to the bottom of the 6th oval ring = 40 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 + 4
Number of oval rings x 12 + 4 = 280
Number of oval rings x 12 = 280 - 4
Number of oval rings x 12 = 276
Number of oval rings = 276 ÷ 12
Number of oval rings = 23
Number of oval rings that Wendy hung altogether = 23
Answer(s): (a) 40 cm; (b) 23