Answer:
Using my (not very precise) periodic table, I get the mass of Ag as 107.87
Explanation:
This must be a combination of these two isotopes. So the % of the other isotope must be 48.16%.
To work with these percentages in an equation I'll use them as decimals.
So now I can start putting them into an equation:
107.87 = (
106.905
⋅
0.5184
) + (
x
⋅
0.4816
)
Because both of the isotope masses, multiplied by their percentage, would give us the overall average mass.
107.87 = 55.419552 ⋅ ( x ⋅ 0.4816
)
Worked out the brackets that we can work out, and then rearrange to give:
107.87 − 55.419552 = ( x ⋅ 0.4816 )
Again rearrange:
52.450448 = ( x ⋅ 0.4816 )
And final rearranging:
x = 52.450448 - 0.4816
x
=
108.909
(using same sig figs as given in question)
You probably want to work through that again using your periodic table value for Ag.
