Zara started jogging from the park to the nature reserve at a speed of 115 m/min at 7 a.m. Her sister started jogging from the park later. They were beside each other at 7.35 a.m. and her sister reached the nature reserve at 8 a.m. while Zara was still 1500 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the park?
1 h = 60 min

From 7 a.m. to 8 a.m. = 1 h
From 7.35 a.m. to 8 a.m. = 25 min

Distance between the park and the nature reserve
= 60 x 115 + 1500
= 6900 + 1500
= 8400 m

Distance that Zara's sister had to cover to catch up with Zara
= 35 x 115
= 4025 m

Distance that Zara's sister travelled to the nature reserve after catching up with Zara
= 8400 - 4025
= 4375 m

Since Zara's sister jogged 4375 m in 35 min,
Zara's sister average speed
= 4375 ÷ 25
= 175 m/min

Duration that Zara's sister took to jog to the nature reserve
= 8400 ÷ 175
= 48 min

Time that Zara's sister left the park:
48 min before 8 a.m. = 7.12 a.m.

Answer(s): 7.12 a.m.