Andy, Vincent and Rael started walking at the same time from the same starting point round a circular track. Rael walked in the clockwise direction. Andy and Vincent walked in an anti-clockwise direction. Rael took 12 min to complete each round. He met Andy after every 3 minutes. He met Vincent after every 6 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Rael complete in 1 h?
- When Rael and Andy met again at the starting point after 1 h, Vincent had completed 2.7 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Rael completed in 1 h
= 60 ÷ 12
= 5
(b)
Rael took 12 min to complete 1 round
1 min =
112 of circular track = 1 u
12 min =
1212 of circular track = 12 u
Rael's distance is the repeated identity.
Make Rael's distance the same.
Rael's distance : Andy's distance
3 : 12 - 3
3 : 9
Rael's distance : Vincent's distance
6 : 12 - 6
6 : 6
Rael |
Andy |
Vincent |
3x2 |
9x2 |
|
6x1 |
|
6x1 |
6 |
18 |
6 |
The distance of Rael is the repeated identity.
LCM of 3 and 6 = 6
In 1 h
Rael's rounds : Andy's rounds : Vincent's rounds
6 : 18 : 6
Distance that Vincent completed in 1 h = 2.7 km
6 rounds = 2.7 km = 2700 m
1 round = 2700 ÷ 6 = 450 m
Circumference of the circular track = 450 m
Answer(s): (a) 5; (b) 450 m