A painter bought some paint for $500. He paid $x for each litre of paint. He accidentally spilt 5 liters of paint and sold the remainder of the psint for $2/litre more than he paid for it. If he made a profit of $40, find the amount he paid for each litre of paint.

Answer 1

Cost per litre = $x
Number of litres bought = 500/x
Number of litres sold, q = 500/x-5
new sale price per litre = x+2
Total revenue = q*(x+2) = 540
so
(500/x -5 )*(x+2) = 540
Solve for x (cost of paint per litre)
I'll get you started:
Multiply both sides by x
(500-5x)(x+2)=540x
Expand left side using FOIL:
-5x^2+490x+1000 = 540x
Group like terms:
5x²+50x-1000=0
...
remember to reject negative roots of the above quadratic equation.