PSLE Julie hung some identical rings vertically. The thickness of each ring was 2 cm. The figure shows how the rings are connected.
- What was the distance from the top of the 1st ring to the bottom of the 5th ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 210 cm. How many rings did Julie hang altogether?
(a)
Distance of 1 ring = 15 cm = 1 x 13 + 2
Distance of 2 rings = 28 cm = 2 x 13 + 2
Distance of 3 rings = 41 cm = 3 x 13 + 2
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 13 + 2
= 67 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 13 + 2
Number of rings x 13 + 2 = 210
Number of rings x 13 = 210 - 2
Number of rings x 13 = 208
Number of rings = 208 ÷ 13
Number of rings = 16
Number of rings that Julie hung altogether = 16
Answer(s): (a) 67 cm; (b) 16