A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weighs 8 g/cm^3, then the weight of the pipe is: Choose the correct choice from the following.
A) 3.6 kg B) 3.696 kg C) 36 kg D) 36.9 kg E) 3.06 kg
External radius = 4 cm,   Internal radius = 3 cm.   Volume of iron=(22/7	x [(4)^2 - (3)^2] x 21) cm^3   (22/7x 7 x 1 x 21)cm^3   462 cm^3.   Weight of iron = (462 x 8) gm = 3696 gm = 3.696 kg.   ANSWER 3.696 kg
<result>B</result>
A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weighs 8 g/cm^3, then the weight of the pipe is: