How to find the radius of a sphere - ISEE Upper Level Mathematics Achievement

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Question

A wooden ball has a surface area of $900\pi m^2$ .

What is its radius?

Answer

A wooden ball has a surface area of $900\pi m^2$ .

What is its radius?

Begin with the formula for surface area of a sphere:

$SA_{sphere}=4\pi r^2$

Now, plug in our surface area and solve with algebra:

$900 \pi m^2=4\pi r^2$

Get rid of the pi

Divide by 4

Square root both sides to get our answer:

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Question

There is a perfectly spherical weather balloon with a surface area of $900 \pi ft^2$ , what is its radius?

Answer

There is a perfectly spherical weather balloon with a surface area of $900 \pi ft^2$ , what is its radius?

Begin with the formula for surface area of a sphere:

$SA_{sphere}=4 \pi r^2$

Now, set it equal to the given surface area and solve for r:

$900 \pi ft^2=4 \pi r^2$

First divide both sides by $4\pi$ .

Then square root both sides to get our answer:

Compare your answer with the correct one above

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