**9.9** is larger. 

Here is why:

When comparing decimals, you look at the numbers from left to right. 
* Both numbers have a **9** in the whole number spot.
* Moving to the first number after the decimal (the tenths place), 9.**9** has a 9, while 9.**1**1 has a 1. 

Since 9 is bigger than 1, 9.9 is the larger number. It can help to add a zero to the end of 9.9 to make them the same length: comparing **9.90** to **9.11** makes it much easier to see that 9.90 is larger!
