A certain defect (D) is present in about 1 out of 1000 cars during production [P(D)=0.001], and a program of testing is to be carried out using a detection device which gives a positive reading with probability 0.99 for a defective car [P(+/D)=0.99] and with probability 0.05 for a non-defective car [P(+/ND)=0.05]. Then if a randomly selected car has a positive reading, find the probability that it actually does have the defect [P(D/+)].
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