A computer program consists of two blocks written independently by two different programmers.the first block has an error with probability 0.2. the second block has an errorwith probability 0.3. if the program returns an error, what is the probability that there isan error in both blocks?

To work out the probability of both errors occuring, simply multiply the probability of the first error by the probability of the second error. Therefore the probability of both errors occurring is 0.2 * 0.3  =  0.06.