PSLE Vanessa 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 5th ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 157 cm. How many rings did Vanessa hang altogether?
(a)
Distance of 1 ring = 13 cm = 1 x 12 + 1
Distance of 2 rings = 25 cm = 2 x 12 + 1
Distance of 3 rings = 37 cm = 3 x 12 + 1
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 12 + 1
= 61 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 12 + 1
Number of rings x 12 + 1 = 157
Number of rings x 12 = 157 - 1
Number of rings x 12 = 156
Number of rings = 156 ÷ 12
Number of rings = 13
Number of rings that Vanessa hung altogether = 13
Answer(s): (a) 61 cm; (b) 13