I need to know the answer and/or formula

Question

A painter needs to cover the walls of four rooms in two coats of paint. Each room measures 4ft by 8ft, the ceiling is 10 ft high in each room. Each gallon covers 32 square feet. How many gallons of paint does he need?

Answer 1

Assuming we're not painting the ceilings, each room has two walls that are 8 by 10 and two that are 4 by 10.  So the total wall area in each room is:

 

Area of each room = 2*(8*10) + 2*(4*10) = 160 + 80 = 240 square feet

 

There are four rooms, so the area of all four rooms is:

 

Area of all 4 rooms = 4*240 = 960 square feet

 

Each bucket of paint covers 32 square feet, so the painter will need:

 

(960 sq.ft./)(32 sq/ft. per gallon) = 30 gallons