Isotopes in Chemistry

“A sample of magnesium contains two stable isotopes: magnesium-24 (abundance 78.99%) and magnesium-26 (abundance 21.01%). Calculate the average atomic mass of magnesium to one decimal place. Show all work. An element has three isotopes: isotope P with a mass of 30 amu and an abundance of 50%, isotope Q with a mass of 31 amu and an abundance of 30%, and isotope R with a mass of 32 amu and an abundance of 20%. Calculate the average atomic mass of this element to one decimal place. Show all work.”