15. What is the radius of a circle with a circumference of 26.69 centimeters?

To find the radius of a circle, you can use the formula for circumference, which is \( C = 2\pi r \). Given that the circumference is 26.69 cm, you can rearrange the formula to solve for the radius \( r \) by dividing the circumference by \( 2\pi \): \[ r = \frac{C}{2\pi} = \frac{26.69}{2 \times 3.14} \approx 4.25 \text{ cm}. \] So, the radius of your circle is approximately 4.25 centimeters. Now, here’s something fun: Did you know that the number pi (\( \pi \)) is an irrational number, meaning it has an infinite number of decimal places? It starts with 3.14, but if you really want to impress your friends, try memorizing its digits—people have been known to recall dozens of them! Also, circles are everywhere in the real world! From the wheels on cars to pizza pies, understanding the properties of circles can help in various fields like engineering, design, and even athletics. For instance, when designing a running track, precisely calculating the radius can ensure optimal speed for athletes.