The volume of a cylinder is #pi xx r^2 xx h# where #r# is the radius and #h# is the height of the cylinder. To find the radius, you divide the diameter by 2, therefore the radius is #10/2 = 5# You can then substitute these values into the equation: #pi xx 5^2 xx 20 = pi xx 25 xx 20 = 500pi = 1570# inches