Find the percent abundance for hypothetical element isotope 270 Q and 280 Q. Q is 276 amu.?

Question

I am looking for the percent abundance of a hypothetical element. Somewhere I am getting lost. Can somebody break this down for me. When I did it my percentages were off.

Thank you

Answer 1

Set the percentage of 270Q at x; 280 Q would then be 1-x.

276 = 270 * x + 280 (1-x)
276 = 270x + 280 - 280x
-4 = -10x
x = 0.4 or 40%
1-x = 0.6 or 60%

Answer 2

The percent abundance for hypothetical element isotope 270 Q is 40% and 280 Q. is 60%