Question 158729
Part of the trip was along major highways and the rest was along country roads.
 The speed limit is 100km/h on the highways and 80km/h on the other roads. 
He spent a total of 12 hours driving 1050 km. Write a system of equations
 that would allow you to find how much time did he spend on each type of road.
:
Let x = time on highway
Let y = time on country roads
:
The time equation:
x + y = 12
y = (12-x); use for substitution
:
The dist equation; dist = speed * time:
100x + 80y = 1050
;
Substitute (12-x) for y in the above equation; find x
100x + 80(12-x) = 1050
100x + 960 - 80x = 1050
100x - 80x = 1050 - 960
20x = 90
x = {{{90/20}}}
x = 4.5 hrs at 100 km/hr
and
y = 12 - 4.5 = 7.5 hrs at 80 km/hr
;
:
Check solutions by finding the total dist:
100(4.5) + 80(7.5) = 
 450 + 600 = 1050;