Let x be the initial amount of paint Tigran had. Note that Tigran used 25% of the initial amount x. To calculate the 25% of x we simply multiply 0.25 times x as follows
[tex]0.25\cdot x[/tex]This is the amount Tigran used. However, after using it, he was left with 7.2 gallons of paint. So if we add the amount he used (0.25x) to what he had left (7.2) we should get the initial amount (x). This translates to the equation
[tex]7.2+0.25\cdot x=x[/tex]We want to solve this equation for x, so first we start by subtracting 0.25x on both sides, so we get
[tex]7.2=x\text{ -0.25x = 0.75x}[/tex]Now, we divide both sides by 0.75 so we get
[tex]x=\frac{7.2}{0.75}=9.6[/tex]So at the beginning Tigran had 9.6 gallons of paint.
