The average monthly salary of 12 workers and 3 managers in a factory was Rs. 600. When one of the manager whose salary was Rs. 720, was replaced with a new manager, then the average salary of the team went down to 580. What is the salary of the new manager?

Explanation:-

The total salary amount = 15 × 600 = 9000
The salary of the exiting manager = 720.
Therefore, the salary of 12 workers and the remaining 2 managers,
= 9000−720 = 8280
When a new manager joins, the new average salary drops to Rs.580 for the total team of 15 of them.
The total salary for the 15 people i.e., 12 workers, 2 old managers and 1 new manager =580×15 =8700
Therefore, the salary of the new manager is,
9000 - 8700 = 300 less than that of the old manager who left the company, which is equal to 720 - 300 = 420.

Alternatively,

The average salary dropped by Rs.20 for 15 of them.
Therefore, the overall salary has dropped by 15×20=300.
Therefore, the new manager's salary should be Rs.300 less than that of the old manager,
= 720−300 =420.