 Hi and welcome to the session. Let us discuss the following question. Question says 12 defective pens are accidentally mixed with 132 good pens. It is not possible to just look at a pen and tell whether or not it is defective. One pen is taken out at random from this lot. Determine the probability that the pen taken out is a good one. First of all, let us understand that probability of an event E is equal to number of outcomes favorable to event E upon total number of possible outcomes. This is the key idea to solve the given question. Let us now start with the solution. Now we know 12 defective pens are accidentally mixed with 132 good pens. So total number of pens is equal to 12 plus 132. That is 144. Now one pen out of these 144 pens can be drawn in 144 ways. So total number of possible outcomes is equal to 144. We have given that there are 132 good pens. So we can write number of good pens is equal to 132. Now each of the good pen can be drawn in 132 ways. So we get number of outcomes favorable to good pen is equal to 132. We have some key idea. We know probability of an event E is equal to number of outcomes favorable to E upon total number of possible outcomes. Here we have to find the probability of the event that pen taken out is a good pen. So probability that pen taken out is a good one is equal to number of outcomes favorable to good pen upon total number of possible outcomes. Now we know number of outcomes favorable to good pen is equal to 132 and total number of possible outcomes is equal to 144. So we get probability that pen taken out is a good one is equal to 132 upon 144. Now we will cancel common factor 12 from numerator and denominator both and we get probability that pen taken out is a good one is equal to 11 upon 12. So this is our required probability. This completes the session. Have you understood the solution? Take care and have a nice day.