City A and City B is 420 km apart. Daniel left City A for City B at 10.00 a.m. travelling at an average speed of 60 km/h. Sean left City A later than Daniel and caught up with him at 2.00 p.m. Sean was travelling at a speed of 90 km/h.

1. At what time did Sean leave City A?
2. How much later did Daniel arrive in City B than Sean? Express your answer in h as a fraction or mixed number.

(a)
From 10.00 a.m. to 2.00 p.m. = 4 h

Distance that Daniel covered when Sean caught up with Daniel
= 4 x 60
= 240 km

Time that Sean 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 Sean left City A:
2 h 40 min before 2.00 p.m. = 11.20 a.m.

(b)
Remaining distance that they had to cover to reach City B
= 420 - 240
= 180 km

Duration that Sean had to travel before reaching City B
= 180 ÷ 90
= 2 h

Duration that Daniel had to travel before reaching City B
= 180 ÷ 60
= 3 h

Duration that Daniel took to arrive later than Sean in City B
= 3 - 2
= 1 h

Answer(s): (a) 11.20 a.m.; (b) 1 h