Correct Answer - Option 4 : 12 months

**Given:**

Ratio of capital invested = 3 ∶ 2

Ratio of profit shared = 1 ∶ 1

**Concept:**

The ratio of profit is shared in the ratio of capital invested for the given time.

**Calculation:**

∵ The profit is equally divided.

Let the capital of A and B = 3a and 2a

Time of investment of A = 'b' months

∴ 3a × b = 2a × 18 months

⇒ b = (2a × 18)/3a

⇒ b = 12 months