A chemistry student as Agora is calculating the average atomic mass of potassium using the following data.

Isotope k-39 Relative abundance 93.12% atomic mass 38.964 amu.

Isotope k-41 Relative abundance 6.88% atomic mass 40.962 amu.

The student calculated the average atomic mass to be 40.823 amu but it is 39.098 amu on the periodic table. What did the student do incorrectly?