posted by Jimmy .
Re has two natural occuring isotopes 185 Re and 187 Re with an average atomic mass of 186.207 amu. Re is 62.60% 187Re and the atomic mass of 187Re is 186.956 amu. What is the mass of 185 Re
(0.6260*186.956) + (1-0.6260)*x = 186.207
Solve for x.
Note: if 63.60% is one isotope, the other must be 100-62.60 = ? That's what I used above but changed to fractions instead of percent.