Twenty years from now, Arjun will become three times as old as he is now. His present age is :
Let Arjun be x years old now
After 20 years, his age will be x + 20
According to question,
x + 20 = 3x or 3x = x + 20
3x - x = 20
2x = 20
x = 10
Therefore, Arjun's present age is 10 years.