Europium has two stable isotopes, 151 Eu (150.9198 u) and 153 Eu (152.9212 u). The atomic mass given for Eu is 151.9640 u. What is the percent abundance of 153 Eu ??

Answer 1

151.9640 = (150.9198 + x) + (152.9212 + y)
= 150.9198x + (152.92 (1-x))
= 150.9198x + 152.92 -152.92x
= -1.922x + 152.92
151.9640-152.92 = -1.922x = 152.92-152.92
-0.956 = -1.922x
-.0956/-1.922x = -1.922x/-1.922x
0.49739... = x
x = 49.73%
Eu-151 = 49.73%
Eu-153 = 50.27%(since 100%-49.73% = 50.27%)

Answer 2

the setup of the answer is correct. however calculations are wrong