If the sum of numbers is 33 and their difference is 15, the smaller number is ?

Answer: Option A

Let the numbers be x and y
Then,
$$x+y=\mathrm{33.....}(i)$$
And,
$$x-y=\mathrm{15.....}(ii)$$
Solving (i) and (ii), we get :
x = 24 , y = 9
∴ Smaller number = 9