Lithium has 2 isotopes. Find the average atomic mass for Li if 7.5% of Li atoms are 6 Li with a mass of 6.015 amu and 92.5% are 7Li with a mass of 7.016amu.
Show all your math for full credit. Afterwards, ask yourself is it reasonable?

Please help ;)

Question

Lithium has 2 isotopes. Find the average atomic mass for Li if 7.5% of Li atoms are 6 Li with a mass of 6.015 amu and 92.5% are 7Li with a mass of 7.016amu. 
Show all your math for full credit. Afterwards, ask yourself is it reasonable?

Please help ;)

jfraser · Answer

the average atomic mass of any element is not just a plain average, but a weighted average. Do you know how a weighted average works?