The mass of indium113 is 112.9041 amu and the mass of indium115 is 114.9039 amu.
4 Answers

the average mass of Indium is 114.8183 g/mol
let X% = In113
then (100 X%) = In115
114.8183 = X% of (112.9041 amu) + (100X)% of (114.9039 amu)
114.8183 = 112.9041X + 114.9039 – 114.9039X
1.9998 X = 0.0856
X = 0.04280
your answers are
In113 = 4.28 %
In115 = 95.72%
p.s. http://ie.lbl.gov/education/parent/In_iso.htm

Atomic Mass Of Indium

Indium Atomic Mass

Using the “Magic Square” I get Ir^113 = 10% and Ir ^115 = 90%