# percentage of a circle

gastwo | 21:28 Mon 20th Feb 2006 | Science

Evening all. Got bit of a problem. Imagine an LPG tank the shape of an upright spare wheel - I need to draw a line across the face where an 80% level would theoretically be. The answer must be simple maths...

Thanks, Shaun.

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Bit involved, but here we go.

You know the radius of the wheel, so area = pi * r^2

Work out 20% of this area (call it X)

Use this link http://www.mathwords.com/a/area_segment_circle.htm

to work out theta (Thats the thing that looks like an 0 with a line through it)[Area is X from above and you know radius r]

Distance S from centre of circle to edge of chord is

S = r * cos(theta/2)

r-S = the distance down from the top of the circle that you need to draw your line.

Hope that works!

Forgot to say, use the bottom formula on the link, which gives the answer in degrees.
Question Author

Thanks sddsddean - three of us are on night shift - we did have nothing to do. Not any more!!

(all over 50 and trying to remember our maths...)

how can I sleep to-night
Question Author

Mornin [email protected] .We Have got to stay awake!

you as well?

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I will never look at a can of beer again without coming over all mathematical
Question Author
Well [email protected] least you'll be able to work out when you have 80% left in it! (or even 20%)...

If the barman doesn't throw me out I'm going to use another beermat and work out something that goes like :-

E + MC Hammer

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