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/cm3, then the weight of the pipe is:
Pick one
A) 3.6 kg
B) 3.696 kg
C) 36 kg
D) 36.9 kg
E) None
Solution   External radius = 4 cm,   Internal radius = 3 cm.   Volume of iron	=(22/7×(42)-(32)×21)cm3   = (22/7×7 ×1×21)cm3   = 462 cm3.   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/cm3, then the weight of the pipe is: