City R and City S is 420 km apart. Oscar left City R for City S at 11.00 a.m. travelling at an average speed of 70 km/h. Andy left City R later than Oscar and caught up with him at 1.00 p.m. Andy was travelling at a speed of 80 km/h.

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

(a)
From 11.00 a.m. to 1.00 p.m. = 2 h

Distance that Oscar covered when Andy caught up with Oscar
= 2 x 70
= 140 km

Time that Andy took to travel 140 km
= 140 ÷ 80
= 1³₄ h

1 h = 60 min
³₄ h = ³₄ x 60 = 45 min
1³₄ h = 1 h 45 min

Time that Andy left City R:
1 h 45 min before 1.00 p.m. = 11.15 a.m.

(b)
Remaining distance that they had to cover to reach City S
= 420 - 140
= 280 km

Duration that Andy had to travel before reaching City S
= 280 ÷ 80
= 3¹₂ h

Duration that Oscar had to travel before reaching City S
= 280 ÷ 70
= 4 h

Duration that Oscar took to arrive later than Andy in City S
= 4 - 3¹₂
= ¹₂ h

Answer(s): (a) 11.15 a.m.; (b) ¹₂ h