[soulja101]

 Isotopic Abundance ( formula in the book does not work)?
Hydrogen is found primarily as two isotopes in nature: H1 (1.0078u) and H2( 2.0140u) Calculate the percentage abudnace of each isoptope based on hydrogen's average mass. How would i do this.

[FeLiXe]

if the abundance of H1 is x then the average will be: x * 1 + (1-x) * 2

you can solve that for x

[AWK]

if the abundance of H1 is x then the average will be: x * 1 + (1-x) * 2

you can solve that for x

If x is percentage of ¹H the formula is
x * 1.007825 + (100 - x) * 2.014102 = 100 * 1.00794

Note, this formula propagate errors horribly. Use isotopic masses as exact as possible

http://www.iupac.org/publications/pac/2002/pdf/7410x1987.pdf