A man's pension on retirement from service is equal to half the average salary during the last $3\text{ years}$ of his service. His salary from 1-1-1983 is $\text{₹ }380$ per month, with increment of $\text{₹ }40$ due on 1-10-83, 1-10-84 and 1-10-85. If he retires on 1-1-86, what pension does he draw per month?

Let's calculate the man's monthly salary over the last $3\text{ years}$ ($36\text{ months}$) before his retirement on 1-1-1986:
1. **From 1-1-1983 to 30-9-1983 ($9\text{ months}$):**

$$\text{Salary}=\text{₹ }380\text{ per month}$$

$$\text{Total for this period}=380\times 9=\text{₹ }3,420$$

2. **From 1-10-1983 to 30-9-1984 ($12\text{ months}$):**
An increment of $\text{₹ }40$ is added.

$$\text{Salary}=380+40=\text{₹ }420\text{ per month}$$

$$\text{Total for this period}=420\times 12=\text{₹ }5,040$$

3. **From 1-10-1984 to 30-9-1985 ($12\text{ months}$):**
Another increment of $\text{₹ }40$ is added.

$$\text{Salary}=420+40=\text{₹ }460\text{ per month}$$

$$\text{Total for this period}=460\times 12=\text{₹ }5,520$$

4. **From 1-10-1985 to 31-12-1985 ($3\text{ months}$):**
A final increment of $\text{₹ }40$ is added.

$$\text{Salary}=460+40=\text{₹ }500\text{ per month}$$

$$\text{Total for this period}=500\times 3=\text{₹ }1,500$$

Now, let's find the total salary earned during the last $36\text{ months}$:

$$\text{Total Salary}=3420+5040+5520+1500=\text{₹ }15,480$$

The average monthly salary is:

$$\text{Average Monthly Salary}=\frac{15480}{36}=\text{₹ }430$$

The pension is equal to half of this average salary:

$$\text{Pension}=\frac{430}{2}=\text{₹ }215$$