50cm³ will make one balloon touch the ceiling so 1800cm³ will make 1800/50 = <<1800/50=36>>36 balloons touch the ceiling
There are 50 balloons in total so 50-36 = <<50-36=14>>14 balloons will not float since they were filled with ordinary air
There are 36-14 = <<36-14=22>>22 more balloons touching the ceiling than not
#### 22