Three numbers are in the ratio 1:2:3. By adding 5 to each of the numbers then the ratio changes to 2: 3: 4. The smallest number is:

Correct option is A

Let the numbers be x, 2x, and 3x.
After adding 5 to each number, the new numbers are (x + 5), (2x + 5), and (3x + 5).
According to the problem, the new ratio is 2:3:4.
​$$\frac{(x + 5) }{(2x + 5)} = \frac{2 }{ 3}$$​​
3(x + 5) = 2(2x + 5)
3x + 15 = 4x + 10
15 - 10 = 4x - 3x
x = 5