The probability is 30/46 for one calculator having no defects. When the second one is chosen that will be 29/45, the third 28/44, and lastly the fourth will be 27/43. Multiply all of those together and your will get 0.168. If you are looking at the percentage complement it will be 100% - 16.8% = 83.2% chance of at least one defect.
