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CBSE Class 9 Answered

Please solve this! It's Very DIFFICULT!
Asked by sharma.vipul74 | 09 Mar, 2009, 03:48: PM
Expert Answer

total surface area of hollow cylinder = curved suface 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 = 4620sq 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

Answered by | 18 Jun, 2009, 12:42: PM
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