Question

A simple impact crater on the moon has a diameter of 15 kilometers. a complex impact crater has a radius of 30 kilometers. how much greater is the circumference of the complex crater than the simple impact crater?

Answer 1

The general equation for computing the circumference of a circle is $C=\pi d$, where C is the circumference, and d is the diameter. (You might also see the equation as $C=2 \pi r$ where r is the radius, because $d=2r$)

Computing the circumferences of the two circles, we get:
$C_{d=15}=\pi (15)=15\pi$
$C_{d=30}=\pi (30)=30\pi$.

To calculate the ratio of two numbers, we can divide one by the other. You can look at this as "How many times does the denominator fit in the numerator?"
$\frac{C_{d=30}}{C_{d=15}}=\frac{30\pi}{15\pi}=2$
So the circumference of the complex impact crater is 2 times greater than the circumference of the simple impact crater.