PSLE Barbara 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 81 cm. How many rings did Barbara hang altogether?
(a)
Distance of 1 ring = 11 cm = 1 x 10 + 1
Distance of 2 rings = 21 cm = 2 x 10 + 1
Distance of 3 rings = 31 cm = 3 x 10 + 1
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 10 + 1
= 51 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 10 + 1
Number of rings x 10 + 1 = 81
Number of rings x 10 = 81 - 1
Number of rings x 10 = 80
Number of rings = 80 ÷ 10
Number of rings = 8
Number of rings that Barbara hung altogether = 8
Answer(s): (a) 51 cm; (b) 8