speed of train --- x km/h
time for 1st trip = 72/x
new speed = x+6
new time = 72/(x+6)
72/x - 72/(x+6) = 12/60 = 1/5
multiply by 5x(x+6)
360(x+6) - 360x = x(x+6)
360x + 2160 - 360x = x^2 + 6x
x^2 + 6x =2160
x^2 + 6x + 9 = 2160+9
(x+3)^2 = 2169
x+3 = ±√2169 = 46.57 , rejecting the negative answer
x = 43.57 km/h
Find the speed of a train if an increase of 6kph lowers the time for a journey of 72 km by 10 minutes.
3 answers
just one observation: 10 minutes is not 1/5 hour
What is the time in the distance is 72 km in the speed is 6
kph
kph