 Hi and welcome to the session. I am Shashi and I am going to help you to solve the following question. Question is which term of the AP? 3, 8, 13, 18 is 78. First of all let us understand that nth term is equal to A plus n minus 1 multiplied by D where A is the first term of AP and D is the common difference between two consecutive terms. This is the key idea to solve the given question. Let us now start with the solution. We are given the series 3, 8, 13, 18 in the question. Clearly we can see the first term is equal to 3 and the common difference between two consecutive terms is equal to 5. We know nth term A n is equal to A plus n minus 1 multiplied by D. Now A n is equal to 78 as we have to find in the question which term of the AP is 78. So A n is equal to 78 and we have to find the value of n in the given expression. Now substituting the corresponding values in the formula we get 78 is equal to 3 plus n minus 1 multiplied by 5. Now this implies 78 minus 3 is equal to n minus 1 multiplied by 5. Now this further implies 75 is equal to 5 multiplied by n minus 1. This implies n minus 1 is equal to 75 divided by 5. This implies n minus 1 is equal to 15. Now we get n is equal to 15 plus 1. This implies n is equal to 16. Therefore the 16th term of the AP is 78. So our required answer is 16th term. This completes the session. Hope you understood the session. Take care and goodbye.