An element has two common isotopes.89% of its atoms have an atomic mass of 12.09 amu, whereas the other 1.11% have an atomic mass of 13.10 amu.

An element has two common isotopes. 98.89% of its atoms have an atomic mass of 12.09 amu, whereas the other 1.11% have an atomic mass of 13.10 amu. Using the isotopic composition provided, calculate the average atomic mass of the element.