1 is the same as any number over itself
so 1= 10/10
so to solve for the question mark we would subtract 1/10 from both sides of the equations
1/10+?=10/10
if we subtract 1/10 from both sides that leaves us with ? on one side and 9/10 on the other side
so our equation is now ?=9/10
so ? is equal to 9/10