Estimate the length of the radius, if the area of a circle is 750 mm2.

Well, the area of a circle = pi * r^2. You know the area and the value of pi so solve for r (the radius).

750/pi = r^2

Square root (750/pi) = r.

The radius of your circle is 5*square root (30/pi) or approximately 15.45

Since the area of a circle is PiR^2, we need to divide by Pi, then square root the remaining answer.

750/3.14 = 238.85

The sq rt of 238.85 = 15.45

The radius is ~15.5mm or 16mm if rounded.