SOLUTION: A group of workers produce 2000 lamps per month. Their output was increased by 10% which demanded a production increase of 40 lamps per worker. How many workers are there in the gr

Let "n" be the (unknown) number of workers.


Then the rate of work was    lamps per worker per month BEFORE increasing.


From the other side,  the rate of work became    lamps per worker per month AFTER increasing.


From the condition, we know that the difference in the rate of work is 40 lamps per worker per month.


It gives you an equation


     -  = 40,

or

     = 40,

    n =  = 5.


ANSWER.  The number of workers is 5.