Eva started jogging from the market to the park at a speed of 115 m/min at 6 a.m. Her brother started jogging from the market later. They were beside each other at 6.40 a.m. and her brother reached the park at 7 a.m. while Eva was still 1700 m away. If both of them travelled at a constant speed throughout the journey, what time did her brother leave the market?
1 h = 60 min

From 6 a.m. to 7 a.m. = 1 h
From 6.40 a.m. to 7 a.m. = 20 min

Distance between the market and the park
= 60 x 115 + 1700
= 6900 + 1700
= 8600 m

Distance that Eva's brother had to cover to catch up with Eva
= 40 x 115
= 4600 m

Distance that Eva's brother travelled to the park after catching up with Eva
= 8600 - 4600
= 4000 m

Since Eva's brother jogged 4000 m in 40 min,
Eva's brother average speed
= 4000 ÷ 20
= 200 m/min

Duration that Eva's brother took to jog to the park
= 8600 ÷ 200
= 43 min

Time that Eva's brother left the market:
43 min before 7 a.m. = 6.17 a.m.

Answer(s): 6.17 a.m.