I need help in understanding and solving this question

[KayCarter]

When an assembly machine is properly calibrated approximately 5% of the finished products are defective. Periodically the quality control engineer randomly selects 20 products at random and tests them. He will halt the production line to check (and reconfigure, if necessary) the calibration if any of the tested products are defective. Assuming that the machine is properly calibrated, what is the probability that production must be halted?

 

[HallsofIvy]

The production will be halted when any the 20 test items are defective. The probability that any one of the items is NOT defective is 1- 0.05= 0.95. What is the probability that NONE of them are defective?. The probability at least one is defective is 1 minus that.