 Hi and welcome to the session. I am Arsena and I am going to help you with the following question which says if S and T are two sets such that S has 21 elements, T has 32 elements and S in the section T has 11 elements, how many elements does S union T have? So first let us learn that if S and T are two finite sets such that they have some common elements then number of elements in S union T is equal to number of elements in the set S plus number of elements in the set T minus number of elements in the set S intersection T. So with the help of this formula we will find the solution of the above problem, so this is a P idea. Let us now start with the solution we are given that S has 21 elements that is number of elements in the set S is equal to 21, T has 32 elements so number of elements in the set T is equal to 32 and S in the section T has 11 elements that is number of elements in S intersection T is equal to 11 and we have to find that how many elements are there in S union T, so substituting the values in the formula which is number of elements in S union T is equal to number of elements in the set S plus number of elements in the set T minus number of elements in the set S intersection T. So on substituting the values we have 21 minus 32 minus 11 which is further equal to 53 minus 11 which is equal to 42 that is number of elements in S union T is equal to 42. So this completes the solution hope you enjoyed the session take care and bye for now.