At 11 20, Japheth left Town T for Town U, driving at a speed of 81 km/h. At 13 20, David also left Town T for Town U driving at a certain speed. Both of them did not change their speed throughout the journey. At 16 20, both of them passed a boutique that was 162 km away from Town U. How many minutes earlier did David reach Town U than Japheth?
Duration that Japheth travelled from 11 20 to 16 20 = 5 h
Distance that Japheth travelled
= 5 x 81
= 405 km
Distance between Town T and Town U
= 405 + 162
= 567 km
Since David passed the boutique at the same time as Japheth, it means that David travelled 405 km in 3 hours.
David's speed during the journey
= 405 ÷ 3
= 135 km/h
Duration that David took to reach Town U after passing the boutique
= 162 ÷ 135
= 1.2 h
Duration that Japheth took to reach Town U after passing the boutique
= 162 ÷ 81
= 2 h
Difference between the time they took to reach Town U
= 2 - 1.2
= 0.8 h
1 h = 60 min
0.8 h = 0.8 x 60 = 48 min
David reached Town U 48 minutes earlier than Japheth.
Answer(s): 48 min