A SAMPLE OF ANTIMONY, Ar=121.8, WAS ANALYSED AND WAS FOUND TO CONSIST OF 60% OF 121Sb AND ONE OTHER ISOTOPE. DETERMINE THE MASS NUMBER OF THE OTHER ISOTOPE IN THE SAMPLE OF ANTIMONY.

please help I'm really stuck,

4 answers

assume you have 100 grams. It becomes the overused algebra candy mixture problem.

60*121+40*X=121.8*100
solve for x
Thats wrong. The answer is 123
How do you get that though
121.8=(0.6*121)+(0.4*x)
121.8=72.6+0.4x
49.2=0.4x
x=123