Risa and Tommy started off from the same place and drove at uniform speeds in the same direction round a 55 km circular racing track. Risa completed each round in 60 minutes. Tommy took 100 minutes to complete each round.
- How far would Tommy be behind Risa after 1 hour?
- How long after they started would it take Risa to meet Tommy for the first time? Express your answer as a whole or mixed number in h.
(a)
60 min = 1 h
1 min =
160 h
60 min =
6060 h = 1 h
100 min =
10060 h = 1
23 h
Risa's speed
= 55 ÷ 1
= 55 x
11= 55 km/h
Tommy's speed
= 55 ÷ 1
23= 55 x
35= 33 km/h
Distance between Risa and Tommy after 1 hour
= 55 - 33
= 22 km
(b)
LCM of 60 and 100 = 300
300 min =
30060 h = 5 h
Time needed for Risa to meet Tommy for the first time = 5 h
Answer(s): (a) 22 km; (b) 5 h