The given is 860 calculators with a possibility that 9 are defective. To calculate for simple probability, we should have a number of desired outcomes (890) and number of possible outcomes (9). To calculate this, we have: 9 divided by 890 which equals to 0.0104. To get the percentage, we multiply 0.0104 by 100 and we'll have 1.04%. So, there's a 1.04% probability that a calculator chosen at random will be defective.