The area of a circle is given by the following formula:

r is the radius of the circle.
We are given a diameter of 26 feet. Because the area formula uses the radius, we must divide the diameter by 2 to find the radius:

The radius of the swimming pool is 13. Now we can plug in all of our values into the formula:




Because we are rounding to the tenths place, look at the hundredths digit:
530.6
66 > 5
530.66 -> 530.7
The area of the swimming pool rounded to the nearest tenth is
530.7 square feet.