Can anyone help me?!
How many cm$^2$ of skin is needed to make a volleyball ball with a diameter of $30$ cm, if for cutting and sewing $12\%$ of the material is lost?
My attempt was the following:
I used the sphere surface formula:
$S=4\pi r^2 = 4(3,14)(225\text{cm}^2) = 2826 \text{cm}^2$
So, $\frac{12}{100} \cdot 2826 = 339,12cm$
Then, 2826+339,12 = 3165,12 cm
I don’t know if this is the right answer! All help/solutions appreciated. Thanks
Your solution is not quite right, unfortunately. What you have calculated is $12\%$ of the surface area of the volleyball and added that on. Unfortunately, you don't lose $12\%$ of the surface area of the volleyball by cutting and sewing, you lose $12\%$ of the material you started with. Adding $12\%$ of the latter does not account for a loss of $12\%$ of the former. What you would want to solve is:
$0.88x = 2826$
where $x$ is the original fabric. Can you solve it from here?
Aside from this final step, everything else in your solution looks good.