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 4th oval ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 248 cm. How many oval rings did Rachel hang altogether?
(a)
Distance of 1 oval ring = 14 cm = 1 x 13 + 1
Distance of 2 oval rings = 27 cm = 2 x 13 + 1
Distance of 3 oval rings = 40 cm = 3 x 13 + 1
Distance from the top of the 1st oval ring to the bottom of the 4th 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 13 + 1
Number of oval rings x 13 + 1 = 248
Number of oval rings x 13 = 248 - 1
Number of oval rings x 13 = 247
Number of oval rings = 247 ÷ 13
Number of oval rings = 19
Number of oval rings that Rachel hung altogether = 19
Answer(s): (a) 40 cm; (b) 19