Zeph and Ahmad 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, Zeph cycled faster than Ahmad. He arrived at the finishing point 30 minutes before Ahmad who was 10 km behind him. Ahmad 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 Zeph's average speed for the remaining 35 km of the trip in km/h?

(a)
60 min = 1 h
30 min =³⁰₆₀ h = ¹₂ 

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

Time that Ahmad 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 Zeph took for the remaining 35 km of the trip, we need to use the time that Ahmad took subtract that of the time taken for first 10 km and the time that Zeph was faster than Ahmad.

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

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

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