An apple has a peel that is 1cm thick and a total diameter of 12cm. What percentage of volume of the apple is the peel?
I tried $$\frac{\text{volume}(\text{radius of 6})-\text{volume}(\text{radius of 5})}{\text{volume}(\text{radius of 6})}$$ and got 42%. Is this correct?
$$ \frac{\frac{ 4\pi6^3}{3} - \frac{4\pi 5^3}{3}}{\frac{4\pi 6^3}{3}} = \frac{6^3 - 5^3}{6^3} = \frac{216-125}{216} = \frac{91}{216} \approx 0.42 $$ You are right.