Gabby started jogging from the bistro to the park at a speed of 108 m/min at 9 a.m. Her brother started jogging from the bistro later. They were beside each other at 9.35 a.m. and her brother reached the park at 10 a.m. while Gabby was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her brother leave the bistro?
1 h = 60 min

From 9 a.m. to 10 a.m. = 1 h
From 9.35 a.m. to 10 a.m. = 25 min

Distance between the bistro and the park
= 60 x 108 + 1800
= 6480 + 1800
= 8280 m

Distance that Gabby's brother had to cover to catch up with Gabby
= 35 x 108
= 3780 m

Distance that Gabby's brother travelled to the park after catching up with Gabby
= 8280 - 3780
= 4500 m

Since Gabby's brother jogged 4500 m in 35 min,
Gabby's brother average speed
= 4500 ÷ 25
= 180 m/min

Duration that Gabby's brother took to jog to the park
= 8280 ÷ 180
= 46 min

Time that Gabby's brother left the bistro:
46 min before 10 a.m. = 9.14 a.m.

Answer(s): 9.14 a.m.