PSLE Sarah 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 84 cm. How many rings did Sarah hang altogether?
(a)
Distance of 1 ring = 14 cm = 1 x 10 + 4
Distance of 2 rings = 24 cm = 2 x 10 + 4
Distance of 3 rings = 34 cm = 3 x 10 + 4
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 10 + 4
= 54 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 10 + 4
Number of rings x 10 + 4 = 84
Number of rings x 10 = 84 - 4
Number of rings x 10 = 80
Number of rings = 80 ÷ 10
Number of rings = 8
Number of rings that Sarah hung altogether = 8
Answer(s): (a) 54 cm; (b) 8