Ryan, Bobby and Seth started walking at the same time from the same starting point round a circular track. Seth walked in the clockwise direction. Ryan and Bobby walked in an anti-clockwise direction. Seth took 6 min to complete each round. He met Ryan after every 4 minutes. He met Bobby after every 5 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Seth complete in 1 h?
- When Seth and Ryan met again at the starting point after 1 h, Bobby had completed 2.4 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Seth completed in 1 h
= 60 ÷ 6
= 10
(b)
Seth took 6 min to complete 1 round
1 min =
16 of circular track = 1 u
6 min =
66 of circular track = 6 u
Seth's distance is the repeated identity.
Make Seth's distance the same.
Seth's distance : Ryan's distance
4 : 6 - 4
4 : 2
Seth's distance : Bobby's distance
5 : 6 - 5
5 : 1
Seth |
Ryan |
Bobby |
4x5 |
2x5 |
|
5x4 |
|
1x4 |
20 |
10 |
4 |
The distance of Seth is the repeated identity.
LCM of 4 and 5 = 20
In 1 h
Seth's rounds : Ryan's rounds : Bobby's rounds
20 : 10 : 4
Distance that Bobby completed in 1 h = 2.4 km
4 rounds = 2.4 km = 2400 m
1 round = 2400 ÷ 4 = 600 m
Circumference of the circular track = 600 m
Answer(s): (a) 10; (b) 600 m