The area of a circle is A = r^2pi Since the area is equal to 121pi the equation would be, 121pi = r^2. To find r in terms of pi take the square root of 121, to find the radius. Then multiply that by two to get the diameter.
According to the empirical rule, 68% of the population is between -1 and +1 standard deviations. That means that 32% is less than -1 or greater than +1 standard deviations. So half of that, or 16%, is greater than +1 standard deviations.
