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 5th ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 314 cm. How many rings did Gillian hang altogether?
(a)
Distance of 1 ring = 15 cm = 1 x 13 + 2
Distance of 2 rings = 28 cm = 2 x 13 + 2
Distance of 3 rings = 41 cm = 3 x 13 + 2
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 13 + 2
= 67 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 13 + 2
Number of rings x 13 + 2 = 314
Number of rings x 13 = 314 - 2
Number of rings x 13 = 312
Number of rings = 312 ÷ 13
Number of rings = 24
Number of rings that Gillian hung altogether = 24
Answer(s): (a) 67 cm; (b) 24