Average atomic mass of argon (Ar) =
\(\frac{(At.\,mass\,of\,^{36}Ar \times \%Abundance)+(At.\,mass\,of\,^{38}Ar \times \%Abundance)+(At.\,mass\,of\,^{40}Ar \times \%Abundance)}{100}\)
\(=\frac{(35.96755u \times 0.337)+(37.96272u\times 0.063)+(39.9624u \times 99.60)}{100}\)
= 39.947 g mol-1
