Sean started driving from Town C towards Town D at 15 40 at an average speed of 60 km/h. Riordan began driving from Town C towards Town D at 17 20 at an average speed of 100 km/h.

1. At what time did Riordan pass Sean on the road?
2. 1¹₄ hours after passing Sean, Riordan reached Town D. At what time did Sean reach Town D?

(a)
From 15 40 to 17 20 = 1 h 40 min

Time that Sean travelled before Riordan started driving = 1 h 40 min

1 h = 60 min
1 h 40 min = 1⁴⁰₆₀ h = 1²₃ h

Distance that Sean travelled before Riordan started driving
= 1²₃ x 60
= ⁵₃ x 60
= 100 km

Difference between Riordan's and Sean's speed
= 100 - 60
= 40 km/h

Time that Riordan took to catch up with Sean
= 100 ÷ 40
= 2.5 h
= 2 h 30 min

2 h 30 min after 17 20 = 19 50

Time that Riordan passed Sean on the road = 19 50

(b)
1¹₄ h = 1 h 15 min

Total time that Riordan travelled
= 1 h 15 min + 2 h 30 min
= 3 h 45 min

3 h 45 min = 3⁴⁵₆₀h = 3³₄h

Distance between Town C and Town D
= 3³₄ x 100
= 375 km

Time that Sean travelled from Town C to Town D
= 375 ÷ 60
= 6.25 h
= 6 h 15 min

6 h 15 min after 15 40 = 21 55

Time that Sean reached Town D = 21 55

Answer: (a) 19 50; (b) 21 55