This collection of problems provides many different interesting scientific contexts in which to develop the key skills of estimation and approximation, and to decide what units might be appropriate.
Examine these estimates. Do they sound about right?
Are these estimates of physical quantities accurate?
When you change the units, do the numbers get bigger or smaller?
Many physical constants are only known to a certain accuracy. Explore the numerical error bounds in the mass of water and its constituents.
Estimate these curious quantities sufficiently accurately that you can rank them in order of size