What is Avogadro's number and what is it used for?

What is precision?

What is accuracy?

how do you calculate the mass of an isotope if you are given the percent abundance and amu mass of the second isotope as well as the total amu mass?

how do you calculate the number a atoms in a pure sample if you are give the radius of the sphere, and its density?

how do you calculate the percent abundance for two isotopes when given there amu mass?