SOLUTION: peter decides to mix grades of gasoline in his truck. he puts in 12 gallons of regular and 7 gallons of premium for a total cost of $48.21. If premium gas cost .21 cents more per g

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Question 553664: peter decides to mix grades of gasoline in his truck. he puts in 12 gallons of regular and 7 gallons of premium for a total cost of $48.21. If premium gas cost .21 cents more per gallon, what was the price of each grade of gasoline?
Found 2 solutions by josmiceli, mananth:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +r+ = the cost per gallon of regular
Let +p+ = the cost per gallon of premium
given:
+12r+ = cost of regular used
+7p+ = cost of premium used
(1) +12r+%2B+7p+=+48.21+
(2) +p+=+r+%2B+.21+
----------------
Substitute (2) into (1)
(1) +12r+%2B+7%2A%28+r+%2B+.21+%29+=+48.21+
(1) +12r+%2B+7r+%2B+1.47+=+48.21+
(1) +19r+=+48.21+-+1.47+
(1) +19r+=+46.74+
(1) +r+=+2.46+
and since
(2) +p+=+r+%2B+.21+
(2) +p+=+2.67+
Regular is $2.46 per gallon and
premium is $2.67 per gallon
check answer:
(1) +12%2A2.46+%2B+7%2A2.67+=+48.21+
(1) +29.52+%2B+18.69+=+48.21+
(1) +48.21+=+48.21+
OK

Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
regular-------------------- 12 -------------x
premium----------------------7-----------------------(x+0.21)
12*x+7(x+0.21)= 48.21
12x+7x+1.47=48.21
19x=48.21-1.47
19x=46.74
x= 46.74/19
regular $2.46
Premium $2.67 ( add 0.21 to regular price)