PSLE Irene 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 142 cm. How many rings did Irene hang altogether?
(a)
Distance of 1 ring = 12 cm = 1 x 10 + 2
Distance of 2 rings = 22 cm = 2 x 10 + 2
Distance of 3 rings = 32 cm = 3 x 10 + 2
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 10 + 2
= 52 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 10 + 2
Number of rings x 10 + 2 = 142
Number of rings x 10 = 142 - 2
Number of rings x 10 = 140
Number of rings = 140 ÷ 10
Number of rings = 14
Number of rings that Irene hung altogether = 14
Answer(s): (a) 52 cm; (b) 14