Jenson and Tom 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, Jenson cycled faster than Tom. He arrived at the finishing point 40 minutes before Tom who was 10 km behind him. Tom did not change his speed throughout and completed it at 08 30.

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

(a)
60 min = 1 h
40 min =⁴⁰₆₀ h = ²₃ 

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

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

3 h 12 min before 08 30 is 05 18.

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

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

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

Answer(s): (a) 05 18; (b) 20⁵₁₄ km/h