PSLE Joelle hung some identical rings vertically. The thickness of each ring was 1 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 172 cm. How many rings did Joelle hang altogether?
(a)
Distance of 1 ring = 10 cm = 1 x 9 + 1
Distance of 2 rings = 19 cm = 2 x 9 + 1
Distance of 3 rings = 28 cm = 3 x 9 + 1
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 9 + 1
= 46 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 9 + 1
Number of rings x 9 + 1 = 172
Number of rings x 9 = 172 - 1
Number of rings x 9 = 171
Number of rings = 171 ÷ 9
Number of rings = 19
Number of rings that Joelle hung altogether = 19
Answer(s): (a) 46 cm; (b) 19