Let x be the number of $1.50 tiles. Then the number of the $4.00 tiles should be (1000-x). The total cost will be 1.50*x + 4.00*(1000-x) dollars. She wants the average cost would be $2 per square foot:= 2. Solve this equation. 1.50*x + 4.00*(1000-x) = 2*1000 1.5x + 4000 - 4x = 2000 -2.5x = 2000 - 4000 -2.5x = -2000 ===============> x = = 800. ANSWER. 800 tiles per $1.500 and the rest 1000-800 = 200 tiles per $4.00. CHECK. = 2.00 dollars. ! Correct !