City U and City V is 360 km apart. Tommy left City U for City V at 11.00 a.m. travelling at an average speed of 60 km/h. Bobby left City U later than Tommy and caught up with him at 3.00 p.m. Bobby was travelling at a speed of 90 km/h.

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

(a)
From 11.00 a.m. to 3.00 p.m. = 4 h

Distance that Tommy covered when Bobby caught up with Tommy
= 4 x 60
= 240 km

Time that Bobby took to travel 240 km
= 240 ÷ 90
= 2²₃ h

1 h = 60 min
²₃ h = ²₃ x 60 = 40 min
2²₃ h = 2 h 40 min

Time that Bobby left City U:
2 h 40 min before 3.00 p.m. = 12.20 p.m.

(b)
Remaining distance that they had to cover to reach City V
= 360 - 240
= 120 km

Duration that Bobby had to travel before reaching City V
= 120 ÷ 90
= 1¹₃ h

Duration that Tommy had to travel before reaching City V
= 120 ÷ 60
= 2 h

Duration that Tommy took to arrive later than Bobby in City V
= 2 - 1¹₃
= ²₃ h

Answer(s): (a) 12.20 p.m.; (b) ²₃ h