Finding abundance of atomic mass?

Question

How would you do this?

If the only two naturally occurring isotopes of chlorine, C1-35 and C1-37, have relative atomic masses of 34.969u and 36.966u respectively, what must be the approximate abundance of each in nature if the average atomic mass of chlorine is 35.453u?

Answer 1

Use math algebra.
Let the abundance of the atom with mass of 34.969u be x. The abundance of the atom with mass of 36.966u be 1-x.
34.969x + 36.966(1-x) = 35.453
Solve this equation for x.