nr. p+ = 75,2x10la-19/1,6x10-19 = 47 p+
pt A avem n0 = Z + 13 = 47 + 13 = 60
=> Aa (masa atomica a izot. A) = n0 + Z = 60 + 47 = 107 u.a.m.
Ab = Aa + 2 = 107 + 2 = 109 u.a.m.
notam cu c = % de izotop A si d = % de izotop B
=> c + d = 100%
Aa / Ab = 1,0764 => Aa = Ab x1,0764
c = 1,0764d
1,0764d + d = 100 => d = 48,16% izotop B iar diferenta = 51,84% izotop A
=> (51,84x107 + 48,16x109)/100 = 107,96 u.a.m.