Question

Find the surface area of a glazed donut with an outer diameter of 7 cm and an inner diameter of 3 cm. The donut is 2 cm tall

Answer 1

If the outer diameter is 7, then the outer radius is b=7/2.

On the other hand, if the inner diameter is 3, then the inner radius is a= 3/2.

Now, the surface area of a torus (glazed donut) with inner radius a and outer radius b is given by

`SA=\pi^2\mleft(b+a\mright)\mleft(b-a\mright)\text{ =}\pi^2(b^2-a^2)`

Then, applying the data of the problem to the above equation, we can conclude that the surface area of the given glazed donut would be:

`SA=\pi^2(b^2-a^2)=\pi^2(((7)/(2))^2-((3)/(2))^2)=98.69`

so that, the correct answer is:

`SA=98.69\approx98.7`