Vanessa started jogging from the clinic to the garden at a speed of 102 m/min at 7 a.m. Her sister started jogging from the clinic later. They were beside each other at 7.35 a.m. and her sister reached the garden at 8 a.m. while Vanessa was still 1700 m away. If both of them travelled at a constant speed throughout the journey, what time did her sister leave the clinic?
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 clinic and the garden
= 60 x 102 + 1700
= 6120 + 1700
= 7820 m

Distance that Vanessa's sister had to cover to catch up with Vanessa
= 35 x 102
= 3570 m

Distance that Vanessa's sister travelled to the garden after catching up with Vanessa
= 7820 - 3570
= 4250 m

Since Vanessa's sister jogged 4250 m in 35 min,
Vanessa's sister average speed
= 4250 ÷ 25
= 170 m/min

Duration that Vanessa's sister took to jog to the garden
= 7820 ÷ 170
= 46 min

Time that Vanessa's sister left the clinic:
46 min before 8 a.m. = 7.14 a.m.

Answer(s): 7.14 a.m.