# GRE Math : How to find the percentage of a sector from an angle

## Example Questions

### Example Question #1 : Sectors

A circle of radius , for an angle , has an arc length of . What is the angle ?

Explanation:

The formula for an arc length, , of a circle of a given radius, , and a given angle,  is:

Note that  is the circumference of the circle.

Conversely, for a known arc length and unknown angle, this equation can be rewritten as follows:

Plugging in the given values, it is therefore possible to find the missing angle:

### Example Question #33 : Circles

Find the radius of the given circle:

The answer cannot be determined from the information given.

Explanation:

To solve this problem, realize that an inscribed angle (an angle formed by two chords) is equal to twice the central angle formed by connecting the origin to the inscribed angle's endpoints:

Now, the formula for an arc length, , of a circle of a given radius, , and a given angle,  is:

Since the radius is the unknown, this equation can be rewritten as:

Plugging in our values, we find:

### Example Question #1 : Sectors

A given pizza with a -inch diameter has  calories. A baker cuts the pizza using a  angle for each piece. If Susan eats five such pieces, how many calories does she consume? Round to the nearest calorie.

Explanation:

To solve this, notice that one piece of pizza comprises  of the total pie or (reducing)  of a pie. Now, if Susan buys five slices, she gets:

of the pie. If the complete pie contains  calories, she will then eat the following amount of calories:

Rounding, this is  calories.