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 122 cm. How many rings did Xandra hang altogether?
(a)
Distance of 1 ring = 12 cm = 1 x 10 + 2
Distance of 2 rings = 22 cm = 2 x 10 + 2
Distance of 3 rings = 32 cm = 3 x 10 + 2
Distance from the top of the 1st ring to the bottom of the 6th ring
= 6 x 10 + 2
= 62 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 10 + 2
Number of rings x 10 + 2 = 122
Number of rings x 10 = 122 - 2
Number of rings x 10 = 120
Number of rings = 120 ÷ 10
Number of rings = 12
Number of rings that Xandra hung altogether = 12
Answer(s): (a) 62 cm; (b) 12