A sample of element Z, which has two isotopes, is made up of 75% Z-12 and 25% Z-13. Calculate the average atomic mass. Round your answer to TWO PLACES after the decimal. Enter your answer as a number (no units)

Average atomic mass  = 12.25

Explanation:

Percent abundance of Z-12 = 75%

percent abundance of Z-13 = 25%

Average atomic mass = ?

Solution:

Average atomic mass  = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)  / 100

Average atomic mass  = (75×12)+(25×13) /100

Average atomic mass =  900 + 325 / 100

Average atomic mass  = 1225 / 100

Average atomic mass  = 12.25 amu.