ANSWER
80%
EXPLANATION
To make a gallon costing $2.25, let x amount of gas mix with y amount of substitute fuel,
[tex]\begin{gathered} y\text{ + x = 1} \\ y\text{ = 1-x ..............equ 1} \end{gathered}[/tex][tex]3.25\text{ x + 2y = 2.25 ............................equ 2}[/tex]Substitute equation 1 into 2
[tex]\begin{gathered} 3.25x\text{ + 2\lparen1 - x\rparen = 2.25} \\ 3.25x\text{ + 2 - 2x = 2.25} \\ 1.25x\text{ = 0.25} \\ x\text{ = }\frac{0.25}{1.25} \\ x\text{ = 0.2} \end{gathered}[/tex]Determine the percent of substitute fuel
From equation 1:
y = 1 - x
y = 1 - 0.2
y = 0.8 = 80%.
Hence, 80 percent of the mixture must be substitute fuel to bring the cost down to $2.25 per gallon.
