###Human: There was a big sale on cat food at the pet store. 20 people bought cat food that day. The first 8 customers bought 3 cases each. The next four customers bought 2 cases each. The last 8 customers of the day only bought 1 case each. How many cases of cat food were sold?, ### Assistant: The first 8 customers bought 8*3=24 cases
The next 4 customers bought 4*2=8 cases
The last 8 customers bought 8*1=8
In total 24+8+8=40 cases were sold 
 So the answer is :  40