% abundance?

% abundance?
Uranium has an atomic mass equal to 238.0289. It consists of two isotopes: uranuim-235 with an isotopic mass of 235.44 amu and uranium-238 with an isotopic mass of 238.51. How do i calculate the % abundance of the uranium-235 isotope?
I need to know how to do the actual proceedure. If you could just show me how to get it that would be great!
thanks!

Best answer:

Answer by Dr.A
Let x = % abundane Uranium -235
the % abundance of Uranium -238 will be 100 -x

238.0289 = x ( 235.44) + ( 100-x ) 238.51 / 100

23802.89 = x ( 235.44) + 23851 – x(238.51)

48.11 = 3.07 x

x = 15.67 % => U-235
% U -238 = 100 – 15.67 =84.33

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