Question

The height of a hollow cylinder is $14cm$ if external diameter is $16cm$ and total curved surface area of the hollow cylinder is $1320sq.cm$, then its internal diameter is

• A. $14cm$
• B. $16cm$
• C. $7cm$
• D. $8cm$

Answer 1

The correct option is C $7cm$

Given

external radius $r_2=8$, height of cylinder $h=14$

we have,

$2\pi h(r_1+r_2)=1320$

$⟹8+r_1=\frac{1320\times 7}{2\times 22\times 14}$

$⟹r_1=7cm$