Magnesium has three naturally occurring isotopes: 24 Mg (23.985 amu) with 78.99% abundance, 25 Mg (24.986 amu) with 10.00% abundance, and a third with 11.01% abundance. Look up the atomic mass of magnesium, and then calculate the mass of the third isotope.

Answer 1

23.985(0.7899) + 24.986(0.1000) + (x)(0.1101) = mass you look up.
Solve for x.
Check my thinking.

Answer 2

2.311023x

Answer 3

I don't know what 2.311023x stands for but it isn't the mass of the third isotope.