Question 1210251
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I iron pipe has a cross section, the iron being 1cm thick. 
The mass of 1cm3 of cast iron is 7.2g. 
Calculate the mass of a 2metre length of the pipe
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To solve the problem, multiply the cast iron density of 7.2 g/cm^3 by the volume of the metal.


To find the volume of the metal, multiply the cross-section area of the pipe by its length
in consistent units.


To find the area of the cross-section of the pipe, from the greater area of the circle subtract 
the area of the smaller circle.


To find the areas of circles in cross-section, the radii or diameters are needed 
(since the thickness of the pipe is given, any one of the two radii/diameters should be given).


But neither radius nor diameter of the pipe is given in the post, making the problem like 
a three-leg horse.
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I am very disappointed by inaccuracy of the person, who created this three-leg horse problem
and disseminates it in the Internet.


It is inappropriate level to communicate with the tutors, posting them crippled tasks.