Nitrogen has two naturally occurring isotopes, N-14 and N-15. The atomic mass of nitrogen is 14.007 amu. Which isotope is more abundant in nature? Explain

Suppose that:

Mass of N-14 = 14

and Mass of N-15 = 15

fraction N-14 x 14 + fraction N-15 x 15 = 14.007

now ... if the fractions were =, that is if fraction N-14 = fraction N-15 = 0.5, then ...

0.5 x 14 + 0.5 x 15 = 14.5

more N-15 would make that number larger ...

0.3 x 14 + 0.7 x 15 = 14.7

let x = abundance of N-14, then (1-x) = abundance of N-15, and we could solve for x.

(X) x14 + (1-X) x 15 = 14.007

14X + 15 - 15X = 14.007

X = 0.993

the relative abundance of N-14 = 99.3%

the relative abundance of N-15 = 0.7%

So, according to above explanation N-14 is abundant