 Hi and welcome to the session. Let us discuss the following question. Question says complete the following statements. Fourth part is the sum of the probabilities of all the elementary events of an experiment is dash. Let us now start with the solution. Now first of all let us understand what is an elementary event and event having only one outcome of the experiment is called an elementary event. Now let us take one example to understand what is an elementary event. If we are required to find probability of getting a head when a coin is tossed once then we know probability of getting heads is equal to number of outcomes favourable to heads upon total number of all possible outcomes. Now we know number of all possible outcomes is to you know on tossing a coin we get either a heads or a tail. So the number of all possible outcomes is equal to 2. Now we also know that number of outcomes favourable to head that is edge is 1. So we get probability of getting heads is equal to 1 upon 2. Similarly we can also find out probability of getting tail. It is also equal to 1 upon 2 we know number of outcomes favourable to tail is 1 and number of all possible outcomes is equal to 2. So probability of getting tail is equal to 1 upon 2. Now clearly we can see both these events have only one outcome of the experiment. So they are elementary events. Now if we add probability of both the events then we get 1 upon 2 plus 1 upon 2 which is further equal to 1. So we get the sum of the probabilities of all the elementary events of an experiment is 1. So we can fill in this blank 1. So this is our required answer. This completes the session. Hope you understood the solution. Take care and have a nice day.