# Math Help - Finding the radius of a cylinder

1. ## Finding the radius of a cylinder

Hello,
I am a very new member that had not made a new account because I was banned or anything ;-)

Can anyone please show me how to answer the following question: (my exam is tomorrow so please the sooner the better)
Water comes from a cylindrical tank.
When 2 cubic metres of water leave the tank, the level of water in the tank goes down by 1.3 millimeters. Calculate the radius of the tank, in metres, correct to one decimal place.

the answer is r= sqrt(2/pie*0.0013) = 22.1

Thanks
IBstudent, ow sorry I mean IGCSEstudent

Hi IGCSE student.
Since you want an answer in meters change the drop in level to meters.
This drop times the cross sectional area of cylinder in sq meters = 2 cu meters,Solve equation in r radius of cylinder

bjh

3. Try to completely imagine a new cylinder, one which has a:

Height = 0.0013m
Now since volume is: $Volume = \pi Radius^2 * Height$
$2 = \pi x^2 * 0.0013$