Tim, Andy and Rael started walking at the same time from the same starting point round a circular track. Rael walked in the clockwise direction. Tim and Andy walked in an anti-clockwise direction. Rael took 12 min to complete each round. He met Tim after every 2 minutes. He met Andy after every 4 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Rael complete in 1 h?
- When Rael and Tim met again at the starting point after 1 h, Andy had completed 2.2 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 : Tim's distance
2 : 12 - 2
2 : 10
Rael's distance : Andy's distance
4 : 12 - 4
4 : 8
Rael |
Tim |
Andy |
2x2 |
10x2 |
|
4x1 |
|
8x1 |
4 |
20 |
8 |
The distance of Rael is the repeated identity.
LCM of 2 and 4 = 4
In 1 h
Rael's rounds : Tim's rounds : Andy's rounds
4 : 20 : 8
Distance that Andy completed in 1 h = 2.2 km
8 rounds = 2.2 km = 2200 m
1 round = 2200 ÷ 8 = 275 m
Circumference of the circular track = 275 m
Answer(s): (a) 5; (b) 275 m