John and Lee took part in a 24 km marathon. John ran half the distance at a speed of 10 km/h and ran slower for the rest of the way at a speed of 8 km/h. Lee ran half his total time at 12 km/h and ran slower for the rest of the time at 10 km/h. If they started the marathon at 3.30 a.m., at what time would each of them finish?
- John
- Lee
(a)
Half of the 24 km marathon = 24 ÷ 2 = 12 km
Time taken by John for the first half of the marathon
= 12 ÷ 10
= 1
15 h
Time taken by John for the last half of the marathon
= 12 ÷ 8
= 1
12 h
Total time taken by John
= 1
15 + 1
12= 2
710 h
1 h = 60 min
710 h =
710 x 60 = 42 min
2
710 h = 2 h 42 min
2 h 42 min after 3.30 a.m. = 6.12 a.m.
Time that John would finish the marathon = 6.12 a.m.
(b)
Time taken by Lee for the first half of the marathon
= 12 ÷ 12
= 1 h
Time taken by Lee for the last half of the marathon
= 12 ÷ 10
= 1
15 h
Total time taken by Lee
= 1 + 1
15 = 2
15 h
1 h = 60 min
15 h =
15 x 60 = 12 min
2
15 h = 2 h 12 min
2 h 12 min after 3.30 a.m. = 5.42 a.m.
Time that Lee would finish the marathon = 5.42 a.m.
Answer(s): (a) 6.12 a.m.; (b) 5.42 a.m.