The average monthly salary of 19 members of a group is Rs 16,000. One more member with a monthly salary of Rs 20,000 joins the group. What is the new average monthly salary of the group?

Introduction:
Adding one new data point shifts the average depending on how the new value compares with the old average. Compute the old total, add the newcomer's salary, then divide by the new headcount.

Given Data / Assumptions:
Old average (19 members) = Rs 16,000. New member's salary = Rs 20,000. New headcount = 20.

Concept / Approach:
New average = (Old total + newcomer) / New headcount. Old total = 19 * 16,000.

Step-by-Step Solution:
Old total = 19 * 16,000 = Rs 304,000. New total = 304,000 + 20,000 = Rs 324,000. New average = 324,000 / 20 = Rs 16,200.

Verification / Alternative check:
Since 20,000 is 4,000 above the old average, the increase in average should be 4,000 / 20 = 200. Old average 16,000 + 200 = 16,200, matching the calculation.

Why Other Options Are Wrong:
18,250 and 18,000: Far too high for a single addition of 20,000 to a base near 16,000. 16,250: Does not match the exact computation. 16,000: The average must rise because 20,000 exceeds 16,000.

Common Pitfalls:
Averaging 16,000 and 20,000 without weighting by the 19 existing members. Always use totals and the new count.

Final Answer:
The new average salary is Rs 16,200 per month.