Atomic Abundance?

Question

Naturally occuring carbon consists of two isotopes carbon-12 and carbon-14. What are the percent abundances of the two isotopes in a sample of carbon whose atomic mass is 12.011 amu?

Answer 1

Algebra!!

let x = C-12 %
let (1.00 - x) = C-14 %

(12)(x) + (14)(1.00-x) = 12.011

12x + 14 - 14x = 12.011

2x = 1.989

x = 0.9945 or 99.45 % C-12

1-x = .0055 or .55 % C-14