Hint: Here to solve this problem we need to have knowledge about basic simplification. We proceed with the solution by applying the condition given in the question.
Let us consider the age of Ajay = x
Here it is given that Ajay is younger than Vijay by 5 years
Therefore Vijay’s age = x+5
It is also mentioned that sum of their ages is 25
Therefore we say that
\Rightarrow x + (x + 5) = 25 \\
\Rightarrow 2x + 5 = 25 \\
\Rightarrow 2x = 20 \\
\Rightarrow x = 10 \\
Here we considered the age of Ajay as x.
Hence Ajay’s age =10 years
Option B is the correct answer.
NOTE: This problem is a simple age calculation problem. In this problem we have to find the age of a given person, so we have considered his age as x later we have applied the given condition to the person's age and on further simplification we the x value which is nothing but person age (answer).