PSLE Xuan 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 4th ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 171 cm. How many rings did Xuan hang altogether?
(a)
Distance of 1 ring = 11 cm = 1 x 10 + 1
Distance of 2 rings = 21 cm = 2 x 10 + 1
Distance of 3 rings = 31 cm = 3 x 10 + 1
Distance from the top of the 1st ring to the bottom of the 4th ring
= 4 x 10 + 1
= 41 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 10 + 1
Number of rings x 10 + 1 = 171
Number of rings x 10 = 171 - 1
Number of rings x 10 = 170
Number of rings = 170 ÷ 10
Number of rings = 17
Number of rings that Xuan hung altogether = 17
Answer(s): (a) 41 cm; (b) 17