Q. 8

# The external surface area of a hollow cylinder is 540 πsq.cm. Its internal diameter is 16 cm and height is 15 cm. Find the total surface area.

Answer :

__Given__ : External surface area of hollow cylinder = CSA_{ext} = 540 cm^{2}

Internal diameter = d = 16 cm

Height of the hollow cylinder = h = 15 cm

__To find__ : Total surface area = TSA of hollow cylinder = ?

__Formula__ : r =

CSA of cylinder = 2rh

__Solution__ : Internal radius of cylinder = r = = = 8 cm

Internal surface area of hollow cylinder = CSA_{int} = 2πrh

= 2π × 8 × 15

= 16π × 15 = 240π cm^{2}

TSA of hollow cylinder = CSA_{ext} + CSA_{int} = 540 + 240

= 780 cm^{2}

∴ The total surface area of the hollow cylinder is 780 cm^{2}.

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