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    				| 1. | 
                                    A hollow cylindrical tube open at both end is made of iron 2 cm thick. If the external diameter be 50 cm and the length of the tube is 210 cm, find the number of cubic cm of iron in it. | 
                            
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Answer» Solution :External radius (R) = 25 cm  Internal radius (r) = (25-2)= 23 cm VOLUME of IRON = `pi h(R^2-r^2)` = `(22)/7 xx 210 xx (25^2-23^2)` =`63360 cm^2`  | 
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