chemistry
posted by joan .
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 ??

y = fraction Eu 151
then 1y = fraction Eu 153

y(150.9198) + (1y)(152.9212) = 151.9640
Solve for y and 1y.