PSLE Rachel 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 6th ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 241 cm. How many rings did Rachel hang altogether?
(a)
Distance of 1 ring = 13 cm = 1 x 12 + 1
Distance of 2 rings = 25 cm = 2 x 12 + 1
Distance of 3 rings = 37 cm = 3 x 12 + 1
Distance from the top of the 1st ring to the bottom of the 6th ring
= 6 x 12 + 1
= 73 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 12 + 1
Number of rings x 12 + 1 = 241
Number of rings x 12 = 241 - 1
Number of rings x 12 = 240
Number of rings = 240 ÷ 12
Number of rings = 20
Number of rings that Rachel hung altogether = 20
Answer(s): (a) 73 cm; (b) 20