PSLE Mary 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 182 cm. How many rings did Mary hang altogether?
(a)
Distance of 1 ring = 11 cm = 1 x 9 + 2
Distance of 2 rings = 20 cm = 2 x 9 + 2
Distance of 3 rings = 29 cm = 3 x 9 + 2
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 9 + 2
= 47 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 9 + 2
Number of rings x 9 + 2 = 182
Number of rings x 9 = 182 - 2
Number of rings x 9 = 180
Number of rings = 180 ÷ 9
Number of rings = 20
Number of rings that Mary hung altogether = 20
Answer(s): (a) 47 cm; (b) 20