PSLE Erika 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 163 cm. How many rings did Erika hang altogether?
(a)
Distance of 1 ring = 10 cm = 1 x 9 + 1
Distance of 2 rings = 19 cm = 2 x 9 + 1
Distance of 3 rings = 28 cm = 3 x 9 + 1
Distance from the top of the 1st ring to the bottom of the 4th ring
= 4 x 9 + 1
= 37 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 9 + 1
Number of rings x 9 + 1 = 163
Number of rings x 9 = 163 - 1
Number of rings x 9 = 162
Number of rings = 162 ÷ 9
Number of rings = 18
Number of rings that Erika hung altogether = 18
Answer(s): (a) 37 cm; (b) 18