1. The problem statement, all variables and given/known data Simple question, but I don't know how to correctly approach it. How many drops of water are in all the oceans on earth? Assume that 1cm^3 contains 25 drops of water. 2. Relevant equations The average depth of the ocean is 4 km. I know I will have to convert to cm. Radius of Earth: 6400 km About 70% of the earth is covered by oceans. 3. The attempt at a solution Need help setting up the problem correctly. I've tried various things. I'm not sure if I have to use the surface area of a sphere or the volume of a sphere. I have to subtract the depth of the oceans (4km) from 6400km...?