Zoe started jogging from the market to the garden at a speed of 115 m/min at 5 a.m. Her cousin started jogging from the market later. They were beside each other at 5.40 a.m. and her cousin reached the garden at 6 a.m. while Zoe was still 1700 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the market?
1 h = 60 min

From 5 a.m. to 6 a.m. = 1 h
From 5.40 a.m. to 6 a.m. = 20 min

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

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

Distance that Zoe's cousin travelled to the garden after catching up with Zoe
= 8600 - 4600
= 4000 m

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

Duration that Zoe's cousin took to jog to the garden
= 8600 ÷ 200
= 43 min

Time that Zoe's cousin left the market:
43 min before 6 a.m. = 5.17 a.m.

Answer(s): 5.17 a.m.