Charlie, Andy and Jack started walking at the same time from the same starting point round a circular track. Jack walked in the clockwise direction. Charlie and Andy walked in an anti-clockwise direction. Jack took 12 min to complete each round. He met Charlie after every 3 minutes. He met Andy after every 6 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Jack complete in 1 h?
- When Jack and Charlie met again at the starting point after 1 h, Andy had completed 2.4 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Jack completed in 1 h
= 60 ÷ 12
= 5
(b)
Jack took 12 min to complete 1 round
1 min =
112 of circular track = 1 u
12 min =
1212 of circular track = 12 u
Jack's distance is the repeated identity.
Make Jack's distance the same.
Jack's distance : Charlie's distance
3 : 12 - 3
3 : 9
Jack's distance : Andy's distance
6 : 12 - 6
6 : 6
Jack |
Charlie |
Andy |
3x2 |
9x2 |
|
6x1 |
|
6x1 |
6 |
18 |
6 |
The distance of Jack is the repeated identity.
LCM of 3 and 6 = 6
In 1 h
Jack's rounds : Charlie's rounds : Andy's rounds
6 : 18 : 6
Distance that Andy completed in 1 h = 2.4 km
6 rounds = 2.4 km = 2400 m
1 round = 2400 ÷ 6 = 400 m
Circumference of the circular track = 400 m
Answer(s): (a) 5; (b) 400 m