Easy percentage prob (for pro) hahah

[geffman1]

Homework Statement

Lithium has an average atomic weight of 6.941. If the only two stable
isotopes have mass numbers of 6.015 and 7.016, what is the natural
percent abundance of the heavier isotope?

Homework Equations

any help would be good. thanks ( ican do it easy when they give percent but this is different

The Attempt at a Solution

 

[tiny-tim]

Lithium has an average atomic weight of 6.941. If the only two stable
isotopes have mass numbers of 6.015 and 7.016, what is the natural
percent abundance of the heavier isotope?

Hi geffman1!

General technique … give the answer a letter, and use that letter to get an equation.

in this case, call the proportion of the heavier isotope "x" (so the proportion of the lighter isotope is 1 - x), and write an equation.