City T and City U is 432 km apart. Billy left City T for City U at 9.00 a.m. travelling at an average speed of 72 km/h. Oscar left City T later than Billy and caught up with him at 11.00 a.m. Oscar was travelling at a speed of 108 km/h.

1. At what time did Oscar leave City T?
2. How much later did Billy arrive in City U than Oscar? Express your answer in h as a fraction or mixed number.

(a)
From 9.00 a.m. to 11.00 a.m. = 2 h

Distance that Billy covered when Oscar caught up with Billy
= 2 x 72
= 144 km

Time that Oscar took to travel 144 km
= 144 ÷ 108
= 1¹₃ h

1 h = 60 min
¹₃ h = ¹₃ x 60 = 20 min
1¹₃ h = 1 h 20 min

Time that Oscar left City T:
1 h 20 min before 11.00 a.m. = 9.40 a.m.

(b)
Remaining distance that they had to cover to reach City U
= 432 - 144
= 288 km

Duration that Oscar had to travel before reaching City U
= 288 ÷ 108
= 2²₃ h

Duration that Billy had to travel before reaching City U
= 288 ÷ 72
= 4 h

Duration that Billy took to arrive later than Oscar in City U
= 4 - 2²₃
= 1¹₃ h

Answer(s): (a) 9.40 a.m.; (b) 1¹₃ h