15.6.20 Definition and properties of probability

Problem: Out of 1000 lamps 250 belong to the \( 1^{\text {st }} \) batch, 350 belong to the \( 2^{\text {nd }} \) one and 400 to the \( 3^{\text {rd }} \) batch. In the \( 1^{\text {st }} \) batch \( 4 \% \) of the lamps have a defect, in the \( 2^{\text {nd }} \) batch \( 5 \% \) have a defect, and in the \( 3^{\text {rd }} 6 \% \) of the lamps have a defect. A lamp is chosen randomly. Find the probability that the chosen lamp has a defect.