PSLE Tammy 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 6th ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 110 cm. How many rings did Tammy hang altogether?
(a)
Distance of 1 ring = 11 cm = 1 x 9 + 2
Distance of 2 rings = 20 cm = 2 x 9 + 2
Distance of 3 rings = 29 cm = 3 x 9 + 2
Distance from the top of the 1st ring to the bottom of the 6th ring
= 6 x 9 + 2
= 56 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 9 + 2
Number of rings x 9 + 2 = 110
Number of rings x 9 = 110 - 2
Number of rings x 9 = 108
Number of rings = 108 ÷ 9
Number of rings = 12
Number of rings that Tammy hung altogether = 12
Answer(s): (a) 56 cm; (b) 12