Natalie started jogging from the farm to the park at a speed of 105 m/min at 9 a.m. Her sister started jogging from the farm later. They were beside each other at 9.41 a.m. and her sister reached the park at 10 a.m. while Natalie was still 1900 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the farm?
1 h = 60 min

From 9 a.m. to 10 a.m. = 1 h
From 9.41 a.m. to 10 a.m. = 19 min

Distance between the farm and the park
= 60 x 105 + 1900
= 6300 + 1900
= 8200 m

Distance that Natalie's sister had to cover to catch up with Natalie
= 41 x 105
= 4305 m

Distance that Natalie's sister travelled to the park after catching up with Natalie
= 8200 - 4305
= 3895 m

Since Natalie's sister jogged 3895 m in 41 min,
Natalie's sister average speed
= 3895 ÷ 19
= 205 m/min

Duration that Natalie's sister took to jog to the park
= 8200 ÷ 205
= 40 min

Time that Natalie's sister left the farm:
40 min before 10 a.m. = 9.20 a.m.

Answer(s): 9.20 a.m.