Zane and Billy started on a 48-km cycling trip at the same time. They cycled at the same speed for first 10 km. For the remaining 38 km, Zane cycled faster than Billy. He arrived at the finishing point 40 minutes before Billy who was 10 km behind him. Billy did not change his speed throughout and completed it at 07 30.

1. At what time did the trip begin? Give the answer in 12-hour format.
2. What was Zane's average speed for the remaining 38 km of the trip in km/h?

(a)
60 min = 1 h
40 min =⁴⁰₆₀ h = ²₃ 

Billy's average speed
= 10 ÷ ²₃
= 15 km/h

Time that Billy took for the trip
= 48 ÷ 15
= 3³₁₅ h
= 3¹₅ h
= 3 h 12 min

3 h 12 min before 07 30 is 04 18.

(b)
To find the time that Zane took for the remaining 38 km of the trip, we need to use the time that Billy took subtract that of the time taken for first 10 km and the time that Zane was faster than Billy.

Time that Zane took for the remaining 38 km of the trip
= 3¹₅ - ²₃ - ²₃
= 1¹³₁₅ h

Zane's average speed
= 38 ÷ 1¹³₁₅
= 20⁵₁₄ km/h

Answer(s): (a) 04 18; (b) 20⁵₁₄ km/h