Question

A sample of 4 different calculators is randomly selected from a group containing 19 that are defective and 36 that have no defects. what is the probability that at least one of the 4 calculators in the sample is defective?

Answer 1

The probability of all calculators having no defects is 16.8%. The probability of at least one defect is the complement of that probability. 
ie an 83.2% probability of at least one defect.