SOLUTION: A motorist covered a journey of 690 km in 8 hours. He covered part of the journey at 90 km/h and the rest at 80 km/h.What was the distance that he covered at 80 km/h?

Algebra ->  Equations -> SOLUTION: A motorist covered a journey of 690 km in 8 hours. He covered part of the journey at 90 km/h and the rest at 80 km/h.What was the distance that he covered at 80 km/h?       Log On


   

Question 1071245: A motorist covered a journey of 690 km in 8 hours. He covered part of the journey at 90 km/h and the rest at 80 km/h.What was the distance that he covered at 80 km/h?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
                      SPEED       TIME         DISTANCE
First part             90           x            90x
Second part            80           y            80y
Totals                              8            690


system%28x%2By=8%2C90x%2B80y=690%29

x=8-y
-
9x%2B8y=69
9%288-y%29%2B8y=69
72-9y%2B8y=69
-y=69-72
y=72-69
highlight%28y=3%29---------time in hours at 80 km/h

Distance done at 80 km/h ?
80%2A3=highlight%28240%29, in kilometers