This question is way over my head, its the last question in my txt book for this chapter and the only one I dont fully understand and get.

Q. 10. A sector of a circle with radius 5cm and an angle of PI/3(as in u know the mathematical pi) subtended at the centre is cut out of cardboard. It is then curved around to form a cone. Find its exact surface area and volume.

answer for surface area is

25 PI / 6

(ive figured surface area out already)

my working

ok i know the exact value of the surface area, but how do i get the volume?

the answer in the back for volume is

V = 125 35 PI

----------------

648 cm cubed

the decimal form of this answer is = 3.585245522

(not 35 is only under the square root just to clarify)

so just figuring out the volume of this stupid cut out sector is my problem now : (

thx all help appreciated