PSLE Tiffany 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 302 cm. How many rings did Tiffany hang altogether?
(a)
Distance of 1 ring = 14 cm = 1 x 12 + 2
Distance of 2 rings = 26 cm = 2 x 12 + 2
Distance of 3 rings = 38 cm = 3 x 12 + 2
Distance from the top of the 1st ring to the bottom of the 6th ring
= 6 x 12 + 2
= 74 cm
(b)
Formula
Distance from the top of the 1st ring to the bottom of the last ring = Number of rings x 12 + 2
Number of rings x 12 + 2 = 302
Number of rings x 12 = 302 - 2
Number of rings x 12 = 300
Number of rings = 300 ÷ 12
Number of rings = 25
Number of rings that Tiffany hung altogether = 25
Answer(s): (a) 74 cm; (b) 25