City F and City G is 420 km apart. Riordan left City F for City G at 7.00 a.m. travelling at an average speed of 60 km/h. Seth left City F later than Riordan and caught up with him at 9.00 a.m. Seth was travelling at a speed of 80 km/h.

1. At what time did Seth leave City F?
2. How much later did Riordan arrive in City G than Seth? Express your answer in h as a fraction or mixed number.

(a)
From 7.00 a.m. to 9.00 a.m. = 2 h

Distance that Riordan covered when Seth caught up with Riordan
= 2 x 60
= 120 km

Time that Seth took to travel 120 km
= 120 ÷ 80
= 1¹₂ h

1 h = 60 min
¹₂ h = ¹₂ x 60 = 30 min
1¹₂ h = 1 h 30 min

Time that Seth left City F:
1 h 30 min before 9.00 a.m. = 7.30 a.m.

(b)
Remaining distance that they had to cover to reach City G
= 420 - 120
= 300 km

Duration that Seth had to travel before reaching City G
= 300 ÷ 80
= 3³₄ h

Duration that Riordan had to travel before reaching City G
= 300 ÷ 60
= 5 h

Duration that Riordan took to arrive later than Seth in City G
= 5 - 3³₄
= 1¹₄ h

Answer(s): (a) 7.30 a.m.; (b) 1¹₄ h