PSLE Irene 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 254 cm. How many rings did Irene hang altogether?
(a)
Distance of 1 ring = 12 cm = 1 x 11 + 1
Distance of 2 rings = 23 cm = 2 x 11 + 1
Distance of 3 rings = 34 cm = 3 x 11 + 1
Distance from the top of the 1st ring to the bottom of the 5th ring
= 5 x 11 + 1
= 56 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 11 + 1
Number of rings x 11 + 1 = 254
Number of rings x 11 = 254 - 1
Number of rings x 11 = 253
Number of rings = 253 ÷ 11
Number of rings = 23
Number of rings that Irene hung altogether = 23
Answer(s): (a) 56 cm; (b) 23