Did you get it right?

The answer is:

⁴⁰Lb:    40 amu x 0.410 =  16.4
⁴²Lb:    42 amu x 0.483 =  20.286
⁴³Lb:    43 amu x 0.107 =    4.601

16.4 + 20.286 + 4.601 = 41.287 amu

Back to the Isotopes and Average Atomic Mass Notes

Go to the Isotopes and Average Atomic Mass Worksheet