In the book 'Chemistry an atoms based approach' , chapter 2 end of chapter problem 2.41,"Vanadium in nature consists of two isotopes: Vanadium-50 and Vanadium-51. Which is more abundant?"

Now I have: 50amu's*x+51amu's*(1-x)=avg amu's form periodic table

50x+51(1-x)=50.9414

50x+51-51x=50.9414

x(50-51)=50.9414-51

x=-.0586/(50-51)

x=-.0586/-1

.0586*10^2=5.86%

and if (1-x) is Vanadium-51 then

1-5.86%=-4.86

However from data sheets I see for Vanadium-50: .250% exact mass 49.946

for Vanadium-51: 99.750% exact mass 51.94

I do not understand this even though my calculations do show Vanadium-51 to be more % abundance it doen't look

doesn't match the data