Question

Naturally occuring boron is 80.20% boron-11 (atomic mass 11.01 amu) and 19.80% of some other isotope. What must the atomic mass of this second isotope be in order to account for the 10.81 amu average atomic mass of boron?
(Write the answer in two decimal places.)

Answer 1

take the weighted average of both isotopes

Answer 2

\((80.2/100)*11.01 + (19.8/100) * x = 10.81\)

solve for \(x\)