Can someone please answer this question for me

Question

Magnesium has two isotopes.

2512Mg which has a mass of 25.2 amu and an abundance of 65.37%.

2312Mg which has a mass of 23.18 amu and an abundance of 34.63%.

Calculate the average atomic mass of Magnesium according to these values.

= amu

Answer 1

Weight the masses by the percentages and add

65.37 % = 0.6537

34.63 % = 0.3463

so (25.2 x 0.6537) + ( 23.18 x 0.3463)