Lucy started jogging from the hypermart to the reservoir at a speed of 96 m/min at 8 a.m. Her brother started jogging from the hypermart later. They were beside each other at 8.35 a.m. and her brother reached the reservoir at 9 a.m. while Lucy was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her brother leave the hypermart?
1 h = 60 min

From 8 a.m. to 9 a.m. = 1 h
From 8.35 a.m. to 9 a.m. = 25 min

Distance between the hypermart and the reservoir
= 60 x 96 + 1800
= 5760 + 1800
= 7560 m

Distance that Lucy's brother had to cover to catch up with Lucy
= 35 x 96
= 3360 m

Distance that Lucy's brother travelled to the reservoir after catching up with Lucy
= 7560 - 3360
= 4200 m

Since Lucy's brother jogged 4200 m in 35 min,
Lucy's brother average speed
= 4200 ÷ 25
= 168 m/min

Duration that Lucy's brother took to jog to the reservoir
= 7560 ÷ 168
= 45 min

Time that Lucy's brother left the hypermart:
45 min before 9 a.m. = 8.15 a.m.

Answer(s): 8.15 a.m.