Riordan, Fred and Glen started walking at the same time from the same starting point round a circular track. Glen walked in the clockwise direction. Riordan and Fred walked in an anti-clockwise direction. Glen took 5 min to complete each round. He met Riordan after every 3 minutes. He met Fred after every 4 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Glen complete in 1 h?
- When Glen and Riordan met again at the starting point after 1 h, Fred had completed 1.5 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Glen completed in 1 h
= 60 ÷ 5
= 12
(b)
Glen took 5 min to complete 1 round
1 min =
15 of circular track = 1 u
5 min =
55 of circular track = 5 u
Glen's distance is the repeated identity.
Make Glen's distance the same.
Glen's distance : Riordan's distance
3 : 5 - 3
3 : 2
Glen's distance : Fred's distance
4 : 5 - 4
4 : 1
Glen |
Riordan |
Fred |
3x4 |
2x4 |
|
4x3 |
|
1x3 |
12 |
8 |
3 |
The distance of Glen is the repeated identity.
LCM of 3 and 4 = 12
In 1 h
Glen's rounds : Riordan's rounds : Fred's rounds
12 : 8 : 3
Distance that Fred completed in 1 h = 1.5 km
3 rounds = 1.5 km = 1500 m
1 round = 1500 ÷ 3 = 500 m
Circumference of the circular track = 500 m
Answer(s): (a) 12; (b) 500 m