Two numbers are in a ratio of 1: 4 and their sum is 50. what is the smaller number?

Let us assume the common ratio to be = x
Then
(1 * x) + (4 * x) = 50
x + 4x = 50
5x = 50
x = 50/5
   = 10
So from the above deduction, we get the common ratio to be equal to 10
Then
The smallest number = 1 * x
                                  = 1 * 10
                                  = 10