Question

Vitellium (Vi) has the following composition:

Vi-188: 187.9122 amu; 10.861%
Vi-191: 190.9047 amu; 12.428%
Vi-193: 192.8938 amu; 76.711%

Based on this data, what can you predict about the average atomic mass of vitellium?

Answer 1

multiply each isotopes mass by it's percent/fractional abundance (to get the weighted average) and add them all up, like this:

(mass of isotope #1) x (% abundance) + (mass isotope #2) x (% abundance) +... = atomic weight
(187.9122x10861)+190.9047x12.428+192.8938x76.711=god knows what