let

x = the age of Iris

y = the age of Ivan

Together, Iris and Ivan are 120 years old:

x + y = 120

Iris is 10 years younger than Ivan:

x = y - 10

by solving the system of equations:

x + y = 120

x = y - 10

we find:

x = 55 years

y = 65 years

click here to see the step by step solution of the system of equations:

Iris is 55 years old while Ivan is 65 years old.