Erika started jogging from the bank to the garden at a speed of 105 m/min at 9 a.m. Her cousin started jogging from the bank later. They were beside each other at 9.40 a.m. and her cousin reached the garden at 10 a.m. while Erika was still 1400 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the bank?
1 h = 60 min

From 9 a.m. to 10 a.m. = 1 h
From 9.40 a.m. to 10 a.m. = 20 min

Distance between the bank and the garden
= 60 x 105 + 1400
= 6300 + 1400
= 7700 m

Distance that Erika's cousin had to cover to catch up with Erika
= 40 x 105
= 4200 m

Distance that Erika's cousin travelled to the garden after catching up with Erika
= 7700 - 4200
= 3500 m

Since Erika's cousin jogged 3500 m in 40 min,
Erika's cousin average speed
= 3500 ÷ 20
= 175 m/min

Duration that Erika's cousin took to jog to the garden
= 7700 ÷ 175
= 44 min

Time that Erika's cousin left the bank:
44 min before 10 a.m. = 9.16 a.m.

Answer(s): 9.16 a.m.