If a metal pipe 10cm long has an external diameter of 12cm and a thickness of 1cm find the volume of the metal used in making the pipe

A.
120(pi)cm^{3} 
B.
110(pi)cm^{3} 
C.
60(pi)cm^{3} 
D.
50(pi)cm^{3}
Correct Answer: Option B
Explanation
The volume of the pipe is equal to the area of the cross section and length.
let outer and inner radii be R and r respectively.
Area of the cross section = (R^{2} – r^{2})
where R = 6 and r = 6 – 1
= 5cm
Area of the cross section = (6^{2} – 5^{2})(pi) = (36 – 25)(pi)cm sq
vol. of the pipe = (pi) (R^{2} – r^{2})L where length (L) = 10
volume = 11(pi) x 10
= 110(pi)cm^{3}