Let x = the first number
x+1 = the second number
The sum of our two numbers is therefore: x + (x+1)
When you subtract 13 from the above you get 18 left over.
So our equation is:
x + (x+1) - 13 = 18
Now we can just solve for x:
x + (x+1) = 31
2x + 1 = 31
2x = 30
x = 15
So our first number is 15 and our second number must be 16.
