Question

sum of two number is 20 if one of them is 10 what is the other number

Answer 1

let the first no. be a x and second be a y
x+y=20
10+y=20
y=10 
the other is also10

Answer 2

other will be 10 only let one number be x other = 10
atgs,
x+10=20
x= 20-10
x=10