Discussion

Explanation:

Let a = 3x and b = x

a + b = 4x and a – b = 2x

a + b : a – b = 4x : 2x = 2 : 1

Alternately,

Apply Componendo & Dividendo, i.e.

If x/y = p/q, then $\frac{x+y}{x-y}=\frac{p+q}{p-q}$

∴ $\frac{a+b}{a-b}=\frac{3+1}{3-1}=\frac{4}{2}=\frac{2}{1}$

Hence, option (a).
 

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