Question

How do you calculate the atomic mass of element X if there are two isotopes of this element (x-24 and x-28) and 75% of all x atoms are x-28 isotopes?

Answer 1

`(24 xx 25%) + (28 xx 75%) = 27`

Explanation:

`75%` of all X atoms are X-28, which means that `25%` of all X atoms are X-24 as there are only 2 isotopes.

Then, you do the mass number multiplied by its percentage, and add those two together and you'll get the atomic mass of that element. If there are more isotopes, just use the same method for all of the isotopes.