Bobby and Charlie took part in a 42 km marathon. Bobby ran half the distance at a speed of 9 km/h and ran slower for the rest of the way at a speed of 6 km/h. Charlie ran half his total time at 10 km/h and ran slower for the rest of the time at 7 km/h. If they started the marathon at 4.30 a.m., at what time would each of them finish?
- Bobby
- Charlie
(a)
Half of the 42 km marathon = 42 ÷ 2 = 21 km
Time taken by Bobby for the first half of the marathon
= 21 ÷ 9
= 2
13 h
Time taken by Bobby for the last half of the marathon
= 21 ÷ 6
= 3
12 h
Total time taken by Bobby
= 2
13 + 3
12= 5
56 h
1 h = 60 min
56 h =
56 x 60 = 50 min
5
56 h = 5 h 50 min
5 h 50 min after 4.30 a.m. = 10.20 a.m.
Time that Bobby would finish the marathon = 10.20 a.m.
(b)
Time taken by Charlie for the first half of the marathon
= 21 ÷ 10
= 2
110 h
Time taken by Charlie for the last half of the marathon
= 21 ÷ 7
= 3 h
Total time taken by Charlie
= 2
110 + 3
= 5
110 h
1 h = 60 min
110 h =
110 x 60 = 6 min
5
110 h = 5 h 6 min
5 h 6 min after 4.30 a.m. = 9.36 a.m.
Time that Charlie would finish the marathon = 9.36 a.m.
Answer(s): (a) 10.20 a.m.; (b) 9.36 a.m.