When visiting his parents, tyler drives at an average speed of 42 km/h through urban areas, and at an average speed of 105 km/h along the motorway. his journey usually takes him 2.5 hours. one day when there is a fog, he sets off 1 hour early and only manages to average 28 km/h in urban areas and 60 km/h on the motorway. he arrives 30 minutes late. how long was tyler journey?
Let x represent the distance Tyler drives at the slower speed, and let y represent the distance at the higher speed. Using time = distance/speed, we can write equations for the total travel time:
x/42 +y/105 = 2.5
x/28 +y/60 = 4.0 . . . . . 1.5 hours more than the usual 2.5 hours
Multiplying the first equation by 210, we have ...
5x +2y = 525
Multiplying the second equation by 420, we get ...
15x +7y = 1680
Subtracting 3 times the first of these equations from the second, we have ...
(15x +7y) -3(5x +2y) = (1680) -3(525)
y = 105
Putting this into the very first equation, we get ...
x/42 + 105/105 = 2.5
x/42 = 1.5 . . . . . . subtract 1
x = 63 . . . . . . . . .multiply by 42.
The total distance to Tyler's parents' house is ...
63 km + 105 km = 168 km