[tex]A_{r}[/tex] = 24.3
The average atomic mass of X is the weighted average of the atomic masses of its isotopes.
We multiply the atomic mass of each isotope by a number representing its relative importance (i.e., its % abundance).
Thus,
0.790 × 24 u = 18.96 u
0.100 × 25 u = 2.50 u
0.110 × 26 u = 2.86 u
TOTAL = 24.3 u
∴ The relative atomic mass of X is 24.3.
