Mass-produced glass bricks are inspected for defects. The probability that a brick has air bubbles is 0.002. If a brick has air bubbles the probability that it is also cracked is 0.5 while the probability that a brick free of air bubbles is cracked is 0.005. What is the probability that a brick chosen at random is cracked? The probability that a brick is discoloured is 0.006. Given that discolouration occurs independently of the other two defects, find the probability that a brick chosen at random has no defects. (O&C)