Equation help

[swim_fan08]

Here is my problem:

Part 1: Calculate the amount of paint needed to paint the walls of a room of the given length and width. It assumes that the paint covers 350 square feet per gallon.

Width=13
Length=15
Height=8

I set my equation up as so: totalSqFt=(2*width + 2*length)* height to find the total square feet, to find out how many gallons of paint will be needed paintNeeded=totalSqFt/350. When I plug in the width, length, and height I get 1.28 gallons.

Part 2: Suppose the room has doors and windows that don't need painting. Ask the customer the number of doors and number of windows in the room, and adjust the total square feet to be painted accordingly. Assume that each door is 18 square feet and each window is 12 square feet. (I have to modify my equation for this part which is what I am stuck on)

Width=13
Length=15
Height=8
Doors=1
Windows=2

With the width being 13, length being 15, height being 8, 1 door, and 2 windows I am suppose to get 1.16 gallons of paint which I am not getting.

 

[Denis]

Your 1.28 gallons is correct, derived from 448 sq.ft. ; 448 / 350 = 1.28

1 door + 2 windows = 18 + 2(12) = 42 sq.ft. ; so new area = 448 - 42 = 406 sq.ft.
And 406 / 350 = 1.16

Hmmm...what did you do? Add 42?

 

[swim_fan08]

I just subtracted 18 and 12 from the total area.

So, now would my equation be: totalSqFt=(2*width + 2*length)* height + (18+12)?

 

[Denis]

WHY do you insist on "12": that's ONE window; problem states there are TWO windows :shock:

 

[swim_fan08]

I am trying to incorporate the 18 and 12 into the equation that I have so that later on I can plug in the numbers like how many windows and doors.


**** Nevermind, I figured out how to write the equation

 

[Denis]

H = height
L = length
W = width
D = number of doors
X = number of windows

Painting area = 2H(L + W) - 18D - 12X

With H=8, L=15, W=13, doors=1, windows=2:
2(8)(15 + 13) - 18(1) - 12(2)

 

[swim_fan08]

Thats the way I did it.