At 11 40, Harry left Town Q for Town R, driving at a speed of 78 km/h. At 13 40, Jack also left Town Q for Town R driving at a certain speed. Both of them did not change their speed throughout the journey. At 16 40, both of them passed a library that was 156 km away from Town R. How many minutes earlier did Jack reach Town R than Harry?
Duration that Harry travelled from 11 40 to 16 40 = 5 h
Distance that Harry travelled
= 5 x 78
= 390 km
Distance between Town Q and Town R
= 390 + 156
= 546 km
Since Jack passed the library at the same time as Harry, it means that Jack travelled 390 km in 3 hours.
Jack's speed during the journey
= 390 ÷ 3
= 130 km/h
Duration that Jack took to reach Town R after passing the library
= 156 ÷ 130
= 1.2 h
Duration that Harry took to reach Town R after passing the library
= 156 ÷ 78
= 2 h
Difference between the time they took to reach Town R
= 2 - 1.2
= 0.8 h
1 h = 60 min
0.8 h = 0.8 x 60 = 48 min
Jack reached Town R 48 minutes earlier than Harry.
Answer(s): 48 min
