1: since 80% of her class has a calculator you know that 20% does not because 100% - 80% = 20%, then from there you can multiply 110 by 0.2 (20% converted into a decimal) and get 22
2: or you could multiply 110 by 0.8 (80% as a decimal), then take that value (88) and subtract it from 110, (110 - 88 = 22)
