Sarah started jogging from the church to the reservoir at a speed of 114 m/min at 9 a.m. Her brother started jogging from the church later. They were beside each other at 9.35 a.m. and her brother reached the reservoir at 10 a.m. while Sarah was still 1900 m away. If both of them travelled at a constant speed throughout the journey, what time did her brother leave the church?
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 church and the reservoir
= 60 x 114 + 1900
= 6840 + 1900
= 8740 m

Distance that Sarah's brother had to cover to catch up with Sarah
= 35 x 114
= 3990 m

Distance that Sarah's brother travelled to the reservoir after catching up with Sarah
= 8740 - 3990
= 4750 m

Since Sarah's brother jogged 4750 m in 35 min,
Sarah's brother average speed
= 4750 ÷ 25
= 190 m/min

Duration that Sarah's brother took to jog to the reservoir
= 8740 ÷ 190
= 46 min

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

Answer(s): 9.14 a.m.