Check my Maths

[Monkeys Fist 41440]

Right then chaps,

I've been asked to price a job which is painting a tubular duct above a swimming pool. To calculate the amount of paint needed, I need to work out the surface area of the duct.

Dimensions are;

duct diameter= 1m (2r)

duct length = 120m. (H)

The formula for surface area of a cylinder is 2(pi r² ) + 2(pi r) H.

(The first part is to calculate the ends of the cylinder, which doesn't apply in this case as the duct starts and finishes at a wall.)

 

So, putting the dimensions into that , I get 2x( 3.14 x 0.5m )x 120 , or more simply 3.14 x 120, which is 376.8m²

 

That's for a straight cylinder. there a a few bends and outlet boxes, so I've added 10m² and rounded it up to get 390m².

 

Firstly, have I used the right formula, secondly, have I calculated it correctly?

 

 

Cheers

Edited March 16, 2012 by Monkeys Fist

[Happy Face 29]

Yeah, the formula is right. To visualise it easily, I just think of it as a rectangle laid out flat (as if you've cut a line down a toilet roll and laid it flat).

 

Height of the rectangle is 120m as you said.

 

Length is just the circumference of the tube. Circumference is Pi * diameter. (3.14 * 1 = 3.14)

 

So your sum of 120 * 3.14 is just the height * length of a rectangle and is spot on.

Edited March 16, 2012 by Happy Face

[Monkeys Fist 41440]

Cheers mate.

[Howmanheyman 31860]

Buy lots of paint. Keep your receipt and take back any unused paint if you wish to avoid any advanced mathematics. No need for thanks.

[Monkeys Fist 41440]

[Kitman 2204]

Buy lots of paint. Keep your receipt and take back any unused paint if you wish to avoid any advanced mathematics. No need for thanks.

 

Genius !