At 11 15, Ian left Town E for Town F, driving at a speed of 78 km/h. At 12 15, Vaidev also left Town E for Town F driving at a certain speed. Both of them did not change their speed throughout the journey. At 15 15, both of them passed a playground that was 156 km away from Town F. How many minutes earlier did Vaidev reach Town F than Ian?

Distance that Ian travelled
= 4 x 78
= 312 km

Distance between Town E and Town F
= 312 + 156
= 468 km

Since Vaidev passed the playground at the same time as Ian, it means that Vaidev travelled 312 km in 3 hours.

Vaidev's speed during the journey
= 312 ÷ 3
= 104 km/h

Duration that Vaidev took to reach Town F after passing the playground
= 156 ÷ 104
= 1.5 h

Duration that Ian took to reach Town F after passing the playground
= 156 ÷ 78
= 2 h

Difference between the time they took to reach Town F
= 2 - 1.5
= 0.5 h

1 h = 60 min
0.5 h = 0.5 x 60 = 30 min

Vaidev reached Town F 30 minutes earlier than Ian.

Answer(s): 30 min