Justin and Carl started on a 45-km cycling trip at the same time. They cycled at the same speed for first 10 km. For the remaining 35 km, Justin cycled faster than Carl. He arrived at the finishing point 30 minutes before Carl who was 10 km behind him. Carl did not change his speed throughout and completed it at 09 25.

1. At what time did the trip begin? Give the answer in 12-hour format.
2. What was Justin's average speed for the remaining 35 km of the trip in km/h?

(a)
60 min = 1 h
30 min =³⁰₆₀ h = ¹₂ 

Carl's average speed
= 10 ÷ ¹₂
= 20 km/h

Time that Carl took for the trip
= 45 ÷ 20
= 2⁵₂₀ h
= 2¹₄ h
= 2 h 15 min

2 h 15 min before 09 25 is 07 10.

(b)
To find the time that Justin took for the remaining 35 km of the trip, we need to use the time that Carl took subtract that of the time taken for first 10 km and the time that Justin was faster than Carl.

Time that Justin took for the remaining 35 km of the trip
= 2¹₄ - ¹₂ - ¹₂
= 1¹₄ h

Justin's average speed
= 35 ÷ 1¹₄
= 28 km/h

Answer(s): (a) 07 10; (b) 28 km/h