Agallon of paint can cover 400 square feet. to the nearest half gallon, find how much paint will be needed to paint two coats on the walls and ceiling of a room that is 20 feet long, 18 feet wide, and 8 feet high. do not include units, enter a number to the nearest half. examples, 7, 7.5, 8, 8.

You'll need to calculate the surface area to be painted.  The room has two ends, 2 sides and 1 ceiling.  The area of the ceiling is 18*20.  The area of the two ends of the room is 2(8*18).  The area of the two long walls is 2(8*20)

Add these areas together:  18*20 + 2*8*18 + 2*8*20, or 968.

That's 968 square feet.  Since each can contains enough paint for 400 square feet of coverage, divide 968 by 400:

968
= 2.42.  This means having to purchase 2.5              (gallons)
400              This answer is accurate to the nearest 0.5.

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.