PSLE Gwen 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 177 cm. How many rings did Gwen 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 6th ring
= 6 x 11 + 1
= 67 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 = 177
Number of rings x 11 = 177 - 1
Number of rings x 11 = 176
Number of rings = 176 ÷ 11
Number of rings = 16
Number of rings that Gwen hung altogether = 16
Answer(s): (a) 67 cm; (b) 16