Chemistry Question about isotopes?

Question

The atomic mass of copper is 63.540 amu. It is composed of two isotopes, Cu-63 and Cu-65, with atomic masses of 62.930 and 64.928 respectively. What is the relative abundance(%) of those isotopes in naturally occuring samples of copper?

Please tell me how to solve this and the answer

Answer 1

by the calculations the answer comes out is abundance is 64.2% and 35.7%.

Answer 2

Ok so, since you dont know the percent you need to use substitution: x and x-1

Line up like this: you know the mass of copper and the masses of the isotopes you are looking for the percent abundance:

63.540amuCu=(62.930)(x)-(64.928)(1-x)

solve: (check my math please im rushing and mentally doing this so it wont be to complete decimals) this should give you an idea:

63.540=62.930x-64.928-64.928x

64.92+63.540=62.930x-64.928x

128.4=1.998x

x=64.2

100-64.2=35.7

so % abundance is 64.2% and 35.7%