Maria an experienced shipping clerk can fill a certain order

Maria, an experienced shipping clerk, can fill a certain order in 11 hours. Felipe , a new clerk, needs 14 hours to do the same job. Working together, how long will it take them to fill the order?

Solution

Maria can fill in 11 hrs --- 1order

So, Maria can fil in 1 hr --- 1/11 of order

Felipe can fill 14 hrs --- 1order

Felipe can fill in 1/14 of order

If together work they can fill in 1hr = 1/11 +1/14 = 25/11*14 = 25/154of an order

Now they can fill i 1 complete order in 154/25 = 6.16 hrs