A paint can holds 2.5litres of paint and is 18cms tall. Work out the radius

A litre is 1000 cm³ 

Volume = pi*r²*h  where r is radius and h is height, so

pi*r²*18 = 2500  (we have to turn the litres into cm³)

Divide both sides by 18pi

r² = 2500/(18pi)

Take the square root of both sides

r = 50/√(18pi)

$${\mathtt{r}} = {\frac{{\mathtt{50}}}{{\sqrt{{\mathtt{18}}{\mathtt{\,\times\,}}{\mathtt{\pi}}}}}} \Rightarrow {\mathtt{r}} = {\mathtt{6.649\: \!038\: \!006\: \!690\: \!545\: \!1}}$$

So the radius is approximately 6.65cm

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I didn't even know there was an answer to this. o.O

Nice Alan!