One of the guest rooms in my house has two walls that are 15'6" by 8 ft, and two that are 12'3" by 8 ft. When buying paint for the walls, I estimated the wall area to be about 450 sq. ft. Find my percent area.

Question

First I need to find the total area of the wall -- I did this by doubling the wall space for each. For the first one I calculated it to be 240'^2 16". For the second I calculated it to be 120'^2 6"
Then I converted the inches into feet as much as I could and that all came to 361'^2 8"

Then to compute the percent error I did 450 ft^2 - 361ft^2 divided by 361ft^2
My answer is 2.4% but the correct answer is 1.4%.

What have I done incorrectly?

Answer 1

2 * 8 (15.5 + 12.25) = 444

(450 - 444) / 444 = .01351 ≈ 1.4%

there appear to be several arithmetic errors in your calculations
... but your method is correct

Answer 2

I guess I don't understand where you are getting the 2 * 8?

Answer 3

Would you see it if Scott had written his calculation as
8*15.5 + 8*15.5 + 8*12.25 + 8*12.25 ?

which is 8*(15.5+15.5+12.25+12.25)
= 8*2(15.5+12.25) , which is what Scott started with.

Answer 4

Yes, I see it now - I wasn't equating the 15'5" to 15 1/2' and the 12'3" to 12.25' - I was doing it in a much harder way - thank you!