The circle shown at right has a diameter of $20$ cm.  

1. What measurement do you need to find in order to calculate the area inside the circle?

   Hint (a):

   Recall the equation for area from the Math Notes box in this lesson.
   $A=r^2\pi$

   More Help (a):

   What measurement is missing in this equation?

2. Find the area inside the circle using the formula $A=r^2\pi$. Write your answer as a product of $r^2$ and $\pi$, and as an approximation using $\pi=3.14$.

   Step 1 (b):

   Diameter = 2 (radius)

   Solve for $r$.

   $20=2r$

   Step 2 (b):

   Substitute the newly calculated radius into the area formula.

   $A=(10)^2\pi$

   Answer (b):

   $314$ cm²