SOLUTION: I can't seem to come up with the correct equation to start this math problem. Could someone please help me? A family has two cars. During one particular week, the first car cons

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Question 1005531: I can't seem to come up with the correct equation to start this math problem. Could someone please help me?
A family has two cars. During one particular week, the first car consumed
30 gallons of gas and the second consumed
40 gallons of gas. The two cars drove a combined total of
2400 miles, and the sum of their fuel efficiencies was
70 miles per gallon. What were the fuel efficiencies of each of the cars that week?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +d+ = distance in miles driven by the
car that consumed 30 gallons of gas
+2400+-+d+ = distance driven by the
car that consumed 40 gallons of gas
-----------------------------------
+d%2F30+ = fuel efficiency of 1st car
+%28+2499+-+d+%29%2F40+ = fuel efficiency of 2nd car
---------------------------------------
+d%2F30+%2B+%28+2400+-+d+%29%2F40+=+70+
Multiply both sides by +1200+
+40d+%2B+30%2A%28+2400+-+d+%29+=+70%2A1200+
+40d+%2B+72000+-+30d+=+84000+
+10d+=+12000+
+d+=+1200+
+2400+-+d+=+2400+-+1200+
+2400+-+d+=+1200+
-------------------
Both cars drove 1200 mi
+d%2F30+=+1200%2F30+
+d%2F30+=+40+
and
++%28+2400+-+d+%29%2F40+=+1200%2F40+
++%28+2400+-+d+%29%2F40+=+30+
----------------------
The 1st car's fuel efficiency was 40 mi/gallon
The 2nd car's fuel efficiency was 30 mi/gallon