The formula for volume of a sphere is:
where r is the radius
Since we are not given the radius, we can just cut the diameter in half, which is the equivalent.
We should end up getting a radius of 5/4
We now need to substitude 1.25 for r
We can change this to 125/64 * 4/3 * π
Simplify further to get 125/16 * 1/3 * π (cross out the 4's)
Multiply and your final volume should be
125/48π in³