How to find the radius of a sphere

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ISEE Upper Level Quantitative Reasoning › How to find the radius of a sphere

Questions 1 - 3
1

A wooden ball has a surface area of .

What is its radius?

Cannot be determined from the information provided

Explanation

A wooden ball has a surface area of .

What is its radius?

Begin with the formula for surface area of a sphere:

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

Get rid of the pi

Divide by 4

Square root both sides to get our answer:

2

There is a perfectly spherical weather balloon with a surface area of , what is its radius?

Explanation

There is a perfectly spherical weather balloon with a surface area of , what is its radius?

Begin with the formula for surface area of a sphere:

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

First divide both sides by .

Then square root both sides to get our answer:

3

The volume of a sphere is one cubic yard. Give its radius in inches.

Explanation

The volume of a sphere with radius is

.

To find the radius in yards, we set and solve for .

yards.

Since the problem requests the radius in inches, multiply by 36:

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