Bunuel wrote:
The city of Cortisville has two gas stations, Petrocort and Cortoline. On a particular day, gasoline at Petrocort was sold for $2.78 per gallon and gasoline at Cortoline was sold for $3.28. If the average price per gallon for gasoline for the entire city that day was $2.99, what percent of all gasoline sold was sold at Cortoline?
A. 42%
B. 43%
C. 44%
D. 46%
E. 47%
Weighted average of groups combined = (group A proportion)(group A average) + (group B proportion)(group B average) + (group C proportion)(group C average) + ...Let x = the percentage of gas sold at Cortoline
This means that 100-x = the percentage of gas sold at Petrocort
As far as PROPORTIONS go, x/100 is the proportion of gas sold at Cortoline
And (100-x)/100 is the proportion of gas sold at Petrocort
Now plug the values into the weighted averages formula.
We get: 2.99 = (x/100)(3.28) + [(100-x)/100][2.78]
Eliminate the fractions by multiplying both sides by 100 to get: 299 = (x)(3.28) + (100-x)[2.78]
Expand to get: 299 = 3.28x + 278 - 2.78x
Simplify: 299 = 0.5x + 278
Subtract 278 from both sides: 21 = 0.5x
Solve: x = 42
Answer: A
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