Sum of two numbers is thrice their difference. Their ratio is :

Answer: Option B

Let the numbers = a, b
According to the question,
a + b = 3 (a - b)
$$\frac{a+b}{a-b}$$   = $$\frac{3}{1}$$
By componendo and dividendo
$$\frac{2a}{2b}$$   = $$\frac{4}{2}$$
$$\frac{a}{b}$$   = $$\frac{2}{1}$$
a : b = 2 : 1