The diameter is 21, so the radius is 10.5. The area of a circle is πr^2, so 10.5^2π, or 110.25π. The pool is filled 9 inches from the top, so it is 3.5 feet - 9 inches high, 9 inches is 0.75 feet, so 2.75 feet filled. Now multiply 110.25π by 2.75 to get 303.1875π and then 952.4916, closer to 952 cubic feet.
When 16 students are playing kickball, there are 16/16 students on the field. After 2 leave, this becomes 16-2/16, therefore 14/16 which is divisible by 2. and therefore 7/8, which the numerator and denominator have no common divisors.
