Rael and David started on a 50-km cycling trip at the same time. They cycled at the same speed for first 5 km. For the remaining 45 km, Rael cycled faster than David. He arrived at the finishing point 20 minutes before David who was 5 km behind him. David did not change his speed throughout and completed it at 08 30.
- At what time did the trip begin? Give the answer in 12-hour format.
- What was Rael's average speed for the remaining 45 km of the trip in km/h?
(a)
60 min = 1 h
20 min =
2060 h =
13 David's average speed
= 5 ÷
13 = 15 km/h
Time that David took for the trip
= 50 ÷ 15
= 3
515 h
= 3
13 h
= 3 h 20 min
3 h 20 min before 08 30 is 05 10.
(b)
To find the time that Rael took for the remaining 45 km of the trip, we need to use the time that David took subtract that of the time taken for first 5 km and the time that Rael was faster than David.
Time that Rael took for the remaining 45 km of the trip
= 3
13 -
13 -
13 = 2
23 h
Rael's average speed
= 45 ÷ 2
23 = 16
78 km/h
Answer(s): (a) 05 10; (b) 16
78 km/h