Question

stefan wants to paint the wall, ceiling and the floor of his bed room. the walls identical and measure 21 feet by 8 1/3 feet. the ceiling and the floor are squares with each side measuring 21 feet
a- if a gallon of paint covers 315 square feet, how many gallons will be required to paint all the walls? ( round to the next whole number)
b- if each gallon cost $24.80, find the cost of the project?

Answer 1

a)

$\bf 4walls\implies 4\left( 21\cdot 8\frac{1}{3} \right)\qquad 8\frac{1}{3}=\cfrac{8\cdot 3+1}{3}=\cfrac{25}{3} \\\\\\ 4\left( 21\cdot \cfrac{25}{3} \right)\implies 4(7\cdot 25)\implies \boxed{700}\\\\ -------------------------------\\\\ \textit{ceiling and floor}\qquad 2(21\cdot 21)\implies \boxed{882}\\\\ -------------------------------\\\\ \textit{total area to be painted}\qquad 700+882\implies 1582\ ft^2 \\\\\\ \textit{a gallon does }315\ ft^2\qquad thus\qquad \cfrac{1582}{315}\textit{ gallons needed}$

b)

how much is that if each gallon is $24.80?  well, just get the product of the amount from a) and 24.80.