PSLE Cathy 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 4th ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 224 cm. How many rings did Cathy hang altogether?
(a)
Distance of 1 ring = 14 cm = 1 x 10 + 4
Distance of 2 rings = 24 cm = 2 x 10 + 4
Distance of 3 rings = 34 cm = 3 x 10 + 4
Distance from the top of the 1st ring to the bottom of the 4th ring
= 4 x 10 + 4
= 44 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 10 + 4
Number of rings x 10 + 4 = 224
Number of rings x 10 = 224 - 4
Number of rings x 10 = 220
Number of rings = 220 ÷ 10
Number of rings = 22
Number of rings that Cathy hung altogether = 22
Answer(s): (a) 44 cm; (b) 22