PSLE Xandra 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 136 cm. How many rings did Xandra hang altogether?
(a)
Distance of 1 ring = 16 cm = 1 x 12 + 4
Distance of 2 rings = 28 cm = 2 x 12 + 4
Distance of 3 rings = 40 cm = 3 x 12 + 4
Distance from the top of the 1st ring to the bottom of the 6th ring
= 6 x 12 + 4
= 76 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 12 + 4
Number of rings x 12 + 4 = 136
Number of rings x 12 = 136 - 4
Number of rings x 12 = 132
Number of rings = 132 ÷ 12
Number of rings = 11
Number of rings that Xandra hung altogether = 11
Answer(s): (a) 76 cm; (b) 11