The information on a Party Balloon kit containing a tank of Helium states how many of each size balloon you can expect to fill from the tank. The label states that the tank will fill THIRTY 9-inch balloons. You plan to use 11-inch balloons instead of 9" ones, so how many can you expect to be able to fill?

Dahhhh, maybe... gosh I don't know. Can't you do the math ?