you an make a system of equations. lets make a the smaller number and b the larger number. The first equation is b+a=19 and the second equation is b-a=10. we know the second equation has to be the larger number minus the smaller number since the differece is a positive number. Know that we have the two equation made the fallowing system of equations:
b+a=19 (add the bottom equation to the top equation)
b-a=10 (b+b=2b, a-a=0, and 19+10=29)
Since the a got canceled out, you can write one equation 2b=29 which means b=29/2. a=19-(29/2) (by plugging the value for b into the equation b+a=19 and solving for a) which means a=9/2.
Since we are looking for the smaller number the answer is 9/2
I hope this helps.