Mary is baking a cake. The recipe calls for 11 cups of sugar and 9 cups of flour. She already put in 12 cups of flour and 10 cups of sugar. How many more cups of sugar does she need to add?
Let's denote the number of cups of sugar that Mary has already put in by x. Then the number of cups of flour that she has already put in is y. 

The recipe calls for 11 cups of sugar and 9 cups of flour. Therefore x+y=11 and y+z=9. 

We know that x=12 and y=10. Therefore z=11-10=1. 

Therefore the answer (numeric) is: 

1