magnesium consists of three naturally occurring isotopes. the percent abundance of these isotopes is: 24mg (79.70%), 25 mg (10.13%), and 26mg (10.07%). the average atomic mass of the three isotopes is 24.3050 amu. if the atomic mass of 25 mg is 24.98584 amu, and 20 mg is 25.98259 amu, calculate the actual atomic mass of 24 mg.