Vincent, Luke and Ben started walking at the same time from the same starting point round a circular track. Ben walked in the clockwise direction. Vincent and Luke walked in an anti-clockwise direction. Ben took 12 min to complete each round. He met Vincent after every 2 minutes. He met Luke after every 4 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Ben complete in 1 h?
- When Ben and Vincent met again at the starting point after 1 h, Luke had completed 2.4 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Ben completed in 1 h
= 60 ÷ 12
= 5
(b)
Ben took 12 min to complete 1 round
1 min =
112 of circular track = 1 u
12 min =
1212 of circular track = 12 u
Ben's distance is the repeated identity.
Make Ben's distance the same.
Ben's distance : Vincent's distance
2 : 12 - 2
2 : 10
Ben's distance : Luke's distance
4 : 12 - 4
4 : 8
Ben |
Vincent |
Luke |
2x2 |
10x2 |
|
4x1 |
|
8x1 |
4 |
20 |
8 |
The distance of Ben is the repeated identity.
LCM of 2 and 4 = 4
In 1 h
Ben's rounds : Vincent's rounds : Luke's rounds
4 : 20 : 8
Distance that Luke completed in 1 h = 2.4 km
8 rounds = 2.4 km = 2400 m
1 round = 2400 ÷ 8 = 300 m
Circumference of the circular track = 300 m
Answer(s): (a) 5; (b) 300 m