Brenda's mother made cookies for 15 guests but 10 guests did not come. If she prepared 30 cookies and each guest had the same number of cookies How many did each of them have?
There were a total of 30 cookies. 
10 guests did not come, so that means that 15 guests came. 
Each guest had the same number of cookies. 

So if we divide 30 by 15, we get 2. So each guest had 2 cookies.