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

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

Distance that Cathy's sister travelled to the nature reserve after catching up with Cathy
= 8740 - 3990
= 4750 m

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

Duration that Cathy's sister took to jog to the nature reserve
= 8740 ÷ 190
= 46 min

Time that Cathy's sister left the mosque:
46 min before 10 a.m. = 9.14 a.m.

Answer(s): 9.14 a.m.