 Hello and welcome to this session. In this session, we discuss the following question which says suppose an electric current flows in a circuit through two switches S1 and S2 as in the given diagram, this diagram. The probability that S1 and S2 work are 1 upon 2 and 6 upon 7 respectively, what is the probability that the current is able to flow from A to B? Let's proceed with the solution now. We have given this diagram in which it is shown that the current flows through A and B through two switches S1 and S2. We have to find the probability that the current is able to flow from A to B. In the question we have given the probability of S1 that is the probability that the switch S1 works and this is given as 1 upon 2. Then we are also given probability of S2 that is the probability that the switch S2 works and this is given as 6 upon 7. Now the required probability that is the probability that the current flows from A to B is equal to the probability that at least the switch S1 or S2 works that is if either of the switches S1 or S2 works then the current will flow from A to B. So, this is equal to 1 minus the probability that neither S1 nor S2 works. This is further equal to 1 minus probability S1 bar and S2 bar. Further this is equal to 1 minus the probability of S1 bar multiplied by the probability of S2 bar. Now we find out the probability of S1 bar. This is equal to 1 minus the probability of S1 which is equal to 1 minus. Now the probability of S1 is 1 upon 2. So, 1 minus 1 upon 2 this is equal to 1 upon 2. So, probability of S1 bar is equal to 1 upon 2. Next we find out the probability of S2 bar that is the switch S2 does not work. This is equal to 1 minus the probability of S2 which is equal to 1 minus. Now probability of S2 is equal to 6 upon 7. So, 1 minus 6 upon 7 would be equal to 1 upon 7. So, probability of S2 bar is equal to 1 upon 7. So, the required probability that the current flows from A to B is equal to 1 minus the probability of S1 bar which is equal to 1 upon 2 multiplied by the probability of S2 bar which is equal to 1 upon 7. And so, this is equal to 1 minus 1 upon 14 which is equal to 13 upon 14. Thus, we say that the probability that the current flows from A to B is equal to 13 upon 14. So, this is our final answer. This completes the session. Hope you have understood the solution of this question.