Xavier, Harry and Bobby started walking at the same time from the same starting point round a circular track. Bobby walked in the clockwise direction. Xavier and Harry walked in an anti-clockwise direction. Bobby took 12 min to complete each round. He met Xavier after every 2 minutes. He met Harry after every 7 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Bobby complete in 1 h?
- When Bobby and Xavier met again at the starting point after 1 h, Harry had completed 2.1 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Bobby completed in 1 h
= 60 ÷ 12
= 5
(b)
Bobby took 12 min to complete 1 round
1 min =
112 of circular track = 1 u
12 min =
1212 of circular track = 12 u
Bobby's distance is the repeated identity.
Make Bobby's distance the same.
Bobby's distance : Xavier's distance
2 : 12 - 2
2 : 10
Bobby's distance : Harry's distance
7 : 12 - 7
7 : 5
Bobby |
Xavier |
Harry |
2x7 |
10x7 |
|
7x2 |
|
5x2 |
14 |
70 |
10 |
The distance of Bobby is the repeated identity.
LCM of 2 and 7 = 14
In 1 h
Bobby's rounds : Xavier's rounds : Harry's rounds
14 : 70 : 10
Distance that Harry completed in 1 h = 2.1 km
10 rounds = 2.1 km = 2100 m
1 round = 2100 ÷ 10 = 210 m
Circumference of the circular track = 210 m
Answer(s): (a) 5; (b) 210 m