Question

three isotopes of argon occur in nature Ar _{18}^{36} , Ar _{18}^{38} and Ar_{18}^{40} , calculate the average atomic mass of argon to two decimal places , given the following relative atomic masses and abundances of each isotopes : argon-36 ( 35.97 u , 0.337%) , argon-38 ( 37.96 u , 0.063%) , argon-40 ( 39.96,99.600%).

Answer 1

Multiply each percent with each mass and add them together.

So argon 36 should be (0.00337)(36)
Argon 38 should be (0.00063)(38)
Argon 40 will be (0.996)(40)

Multiply each one and add each one on top of each one and you will get your average atomic mass.