percentage of a circle

[gastwo]

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.

[sddsddean]

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!

[sddsddean]

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

[gastwo]

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...)

[Hard@it]

how can I sleep to-night

[gastwo]

Mornin Hard@it .We Have got to stay awake!

you as well?

[Hard@it]

I will never look at a can of beer again without coming over all mathematical

[gastwo]

Well Hard@it least you'll be able to work out when you have 80% left in it! (or even 20%)...

[Hard@it]

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