CBSE Class 9 Answered
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