PSLE Usha hung some identical oval rings vertically. The thickness of each oval ring was 1 cm. The figure shows how the oval rings are connected.
- What was the distance from the top of the 1st oval ring to the bottom of the 5th oval ring?
- The distance from the top of the 1st ring to the bottom of the last ring was 277 cm. How many oval rings did Usha hang altogether?
(a)
Distance of 1 oval ring = 13 cm = 1 x 12 + 1
Distance of 2 oval rings = 25 cm = 2 x 12 + 1
Distance of 3 oval rings = 37 cm = 3 x 12 + 1
Distance from the top of the 1st oval ring to the bottom of the 5th oval ring = 37 cm
(b)
Formula
Distance from the top of the 1st oval ring to the bottom of the last oval ring = Number of oval rings x 12 + 1
Number of oval rings x 12 + 1 = 277
Number of oval rings x 12 = 277 - 1
Number of oval rings x 12 = 276
Number of oval rings = 276 ÷ 12
Number of oval rings = 23
Number of oval rings that Usha hung altogether = 23
Answer(s): (a) 37 cm; (b) 23