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
"explanation : external radius = 4 cm , internal radius = 3 cm . volume of iron = [ ( 22 / 7 ) × ( 42 - 32 ) × 21 ] cm 3 = 462 cm 3 weight of iron = ( 462 x 8 ) gm = 3696 gm = 3.696 kg answer : b"
divide(multiply(subtract(volume_cylinder(divide(8, const_2), 21), volume_cylinder(subtract(divide(8, const_2), 1), 21)), 8), const_1000)