PSLE Gillian 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 6th ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 235 cm. How many rings did Gillian hang altogether?
(a)
Distance of 1 ring = 15 cm = 1 x 11 + 4
Distance of 2 rings = 26 cm = 2 x 11 + 4
Distance of 3 rings = 37 cm = 3 x 11 + 4
Distance from the top of the 1st ring to the bottom of the 6th ring
= 6 x 11 + 4
= 70 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 11 + 4
Number of rings x 11 + 4 = 235
Number of rings x 11 = 235 - 4
Number of rings x 11 = 231
Number of rings = 231 ÷ 11
Number of rings = 21
Number of rings that Gillian hung altogether = 21
Answer(s): (a) 70 cm; (b) 21