Elyse started jogging from the grocery store to the reservoir at a speed of 102 m/min at 6 a.m. Her cousin started jogging from the grocery store later. They were beside each other at 6.35 a.m. and her cousin reached the reservoir at 7 a.m. while Elyse was still 1700 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the grocery store?
1 h = 60 min

From 6 a.m. to 7 a.m. = 1 h
From 6.35 a.m. to 7 a.m. = 25 min

Distance between the grocery store and the reservoir
= 60 x 102 + 1700
= 6120 + 1700
= 7820 m

Distance that Elyse's cousin had to cover to catch up with Elyse
= 35 x 102
= 3570 m

Distance that Elyse's cousin travelled to the reservoir after catching up with Elyse
= 7820 - 3570
= 4250 m

Since Elyse's cousin jogged 4250 m in 35 min,
Elyse's cousin average speed
= 4250 ÷ 25
= 170 m/min

Duration that Elyse's cousin took to jog to the reservoir
= 7820 ÷ 170
= 46 min

Time that Elyse's cousin left the grocery store:
46 min before 7 a.m. = 6.14 a.m.

Answer(s): 6.14 a.m.