Davey  and Charlie shared half a box of crackers.  They each had 20 crackers.  How many crackers did they have when the box was full?

I got 80 because 40 is the half of the box.  I got the other half witch would be 40.I got both of the halfs and added them together.  So I got 80 crackers all together.  There would be 80 crackers in all.