1.32 Use the data given in the following table to calculate the molar mass of naturally occurring argon isotopes:

Isotope Isotopic molar mass Abundance
36Ar  35.96755 g mol–1 0.337%
38Ar  37.96272 g mol–1  0.063%
40Ar  39.9624 g mol–1  99.600%

NEETprep answer:  

=35.96755x0.337100+37.96272x0.063100+39.9624x90.60100gmol-1
=0.121+0.024+399802gmol-1
=399.9947gmol-1