PSLE Xandra 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 169 cm. How many rings did Xandra hang altogether?
(a)
Distance of 1 ring = 9 cm = 1 x 8 + 1
Distance of 2 rings = 17 cm = 2 x 8 + 1
Distance of 3 rings = 25 cm = 3 x 8 + 1
Distance from the top of the 1st ring to the bottom of the 6th ring
= 6 x 8 + 1
= 49 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 8 + 1
Number of rings x 8 + 1 = 169
Number of rings x 8 = 169 - 1
Number of rings x 8 = 168
Number of rings = 168 ÷ 8
Number of rings = 21
Number of rings that Xandra hung altogether = 21
Answer(s): (a) 49 cm; (b) 21