Average Isotopic Mass

Silver has two table isotopes. The actual isotopic mass of ¹⁰⁷Ag is 106.9051 amu and the isotopic mass of ¹⁰⁹Ag, 108.9047amu. What is the percent abundance of each isotope?
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The average atomic mass of Ag is 107.8682 (you can look this up).
Let the fraction Ag-109 = x (this is really the % expressed as a decimal fraction)
Then, the fraction of Ag-107 would be 1-x (1 means 100%)
Now set up:
108.9047x + 106.9051(1-x) = 107.8682
(This is an expression for the “weighted average” which is given so we calculate the percent of each isotope)

We simplify the above equation and solve for x,
then we substitute below to get the percents
100x = % of Ag-109
(100)(1-x) = % of Ag-107