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
