Charlie and Sam took part in a 24 km marathon. Charlie ran half the distance at a speed of 8 km/h and ran slower for the rest of the way at a speed of 5 km/h. Sam ran half his total time at 10 km/h and ran slower for the rest of the time at 6 km/h. If they started the marathon at 6.30 a.m., at what time would each of them finish?
- Charlie
- Sam
(a)
Half of the 24 km marathon = 24 ÷ 2 = 12 km
Time taken by Charlie for the first half of the marathon
= 12 ÷ 8
= 1
12 h
Time taken by Charlie for the last half of the marathon
= 12 ÷ 5
= 2
25 h
Total time taken by Charlie
= 1
12 + 2
25= 3
910 h
1 h = 60 min
910 h =
910 x 60 = 54 min
3
910 h = 3 h 54 min
3 h 54 min after 6.30 a.m. = 10.24 a.m.
Time that Charlie would finish the marathon = 10.24 a.m.
(b)
Time taken by Sam for the first half of the marathon
= 12 ÷ 10
= 1
15 h
Time taken by Sam for the last half of the marathon
= 12 ÷ 6
= 2 h
Total time taken by Sam
= 1
15 + 2
= 3
15 h
1 h = 60 min
15 h =
15 x 60 = 12 min
3
15 h = 3 h 12 min
3 h 12 min after 6.30 a.m. = 9.42 a.m.
Time that Sam would finish the marathon = 9.42 a.m.
Answer(s): (a) 10.24 a.m.; (b) 9.42 a.m.