Question

What is the surface area of a cylindrical ring if its outside diameter is 16 mm and its inside diameter is 10 mm? Round your answer to the nearest whole number.

A.92mm^2
B.118mm^2
C.385mm^2
D.123mm^2

Answer 1

D.
`123\ mm^2`

Explanation:

The cylindrical ring has outside diameter of 16 mm and inside diameter of 10 mm.

The area of the outer circle,

`A_(outer)=\pi \cdot (d^2)/(4)=\pi \cdot (16^2)/(4)=64\pi\ mm^2`

The area of the inner circle,

`A_(inner)=\pi \cdot (d^2)/(4)=\pi \cdot (10^2)/(4)=25\pi\ mm^2`

So the area of the ring will be,

`A_(outer)-A_(inner)=64\pi-25\pi=39\pi=122.52\approx 123\ mm^2`

Answer 2

S1=200.96
S2=78.5
Sring=200.96-78.5=122.46 ≈ D.123mm^2