Charlie and Rael took part in a 42 km marathon. Charlie ran half the distance at a speed of 12 km/h and ran slower for the rest of the way at a speed of 5 km/h. Rael ran half his total time at 10 km/h and ran slower for the rest of the time at 10 km/h. If they started the marathon at 7.30 a.m., at what time would each of them finish?
- Charlie
- Rael
(a)
Half of the 42 km marathon = 42 ÷ 2 = 21 km
Time taken by Charlie for the first half of the marathon
= 21 ÷ 12
= 1
34 h
Time taken by Charlie for the last half of the marathon
= 21 ÷ 5
= 4
15 h
Total time taken by Charlie
= 1
34 + 4
15= 5
1920 h
1 h = 60 min
1920 h =
1920 x 60 = 57 min
5
1920 h = 5 h 57 min
5 h 57 min after 7.30 a.m. = 13.27 a.m.
Time that Charlie would finish the marathon = 13.27 a.m.
(b)
Time taken by Rael for the first half of the marathon
= 21 ÷ 10
= 2
110 h
Time taken by Rael for the last half of the marathon
= 21 ÷ 10
= 2
110 h
Total time taken by Rael
= 2
110 + 2
110 = 4
210 h
1 h = 60 min
210 h =
210 x 60 = 12 min
4
210 h = 4 h 12 min
4 h 12 min after 7.30 a.m. = 11.42 a.m.
Time that Rael would finish the marathon = 11.42 a.m.
Answer(s): (a) 13.27 a.m.; (b) 11.42 a.m.