Answers

2016-01-30T21:58:52+05:30
Total surface area of hollow cylinder = 
curved surface area + 2(area of base rings)                                                            = 2h(R+r) + 2(R2 -r2).....................1 also,                                                      = 2(R +r)(h + R  -r)...........................2
total surface area of hollow cylinder = 4620 sq cm
so,
2h(R+r) + 2(R2 -r2) = 4620
area of base rings = 115.5 sq cm
so,       
2h(R+r) = 4620 - 2(115.5)
               
2(R+r) = 4389/7                                          {here   h = 7cm} 
                               =627....................3
now from eq 2              
2(R +r)(h + R  -r) = 4620
                              
(h + R  -r)=4620/627                     {from eq 3}                                     
R  -r = 7.36842 - 7                                      
R  -r = .36842 cm
so thickness of given cylinder = .36842 cm
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