Question

Find the cost of painting a sphere with radius 7cm at the rate of rs 7/sq

Answer 1

Given radius, r = 7 cm
         therefore, CSA = 4 x TT x r^2
                                  = 4 x 22/7 x 7 x 7
                               = 4 x 22 x 7 (since 7 and seven cancelled with each other)
                                  = 88 x 7 = 616 cm^2
                                                = 616 m^2
                                   
Cost of painting 1 m^2 (maybe) = Rs7
  "      "     "          the sphere   = The TSA or the CSA x 7
                                              = 616 x 7
                                               = Rs 4312

:)