A bag contains a certain number of bolts out of which some are 'defective' while the remaining are 'non-defective'. The probability of picking a 'non-defective' bolt is 200% more than picking a 'defective' bolt from the bag. If 40 more 'non-defective' bolts are added to the bag then the probability of picking a 'defective' bolt becomes 20%. Two bolts are picked from the bag before addition, then what is the probability that at most one of the two bolts is 'defective'?