SOLUTION: In one week, Fearless Frank drove 100 miles on the freeway and 150 miles in town. His car consumed 18.2 gallons of gasoline. The next week his journeys took him over 180 miles of f

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: In one week, Fearless Frank drove 100 miles on the freeway and 150 miles in town. His car consumed 18.2 gallons of gasoline. The next week his journeys took him over 180 miles of f      Log On


   



Question 746010: In one week, Fearless Frank drove 100 miles on the freeway and 150 miles in town. His car consumed 18.2 gallons of gasoline. The next week his journeys took him over 180 miles of freeway and 30 miles of local driving, and he used only 10.9 gallons of gas. What were his highway m.p.g. and his local m.p.g.?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The key is to see that ( miles driven ) / ( miles / gallon ) = gallons
I can say:
Let +a+ = mpg on the highway
Let +b+ = mpg in town
(1) +100+%2F+a+%2B+150+%2F+b+=+18.2+
(2) +180+%2F+a+%2B+30+%2F+b+=+10.9+
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(1) +1000+%2F+a+%2B+1500+%2F+b+=+182+
(2) +1800+%2F+a+%2B+300+%2F+b+=+109+
------------------------------
Multiply both sides of (2) by +5+
and subtract (1) from (2)
(2) +9000+%2F+a+%2B+1500+%2F+b+=+545+
(1) +-1000+%2F+a+-+1500+%2F+b+=+-182+
+8000%2A%281%2Fa%29+=+363+
+a+=+8000+%2F+363+
+a+=+22.039+
and
(2) +1800+%2F+22.039+%2B+300+%2F+b+=+109+
(2) +81.673+%2B+300%2Fb+=+109+
(2) +300%2Fb+=+27.327+
(2) +b+=+300+%2F+27.327+
(2) +b+=+10.978+
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His highway m.p.g. was about 22
and his local m.p.g. was about 11
-----------------
check:
(1) +100+%2F+22.039+%2B+150+%2F+10.978+=+18.2+
(1) +4.537+%2B+13.664+=+18.2+
(1) +18.2007+=+18.2+
close enough