 Hello and welcome to the session. Let us understand the following question today. Find the sum of the first 15 multiples of 8. Now let us write the solution. The multiples of 8 are 8, 16, 24, 32, 40 and so on. So we have the AP as 8, 16, 24, 32, 40 and so on. Here we see that A is equal to 8, D is equal to 16 minus 8 which is equal to 8 and N is equal to, since we have to find the sum of first 15 multiples so N is equal to 15. Now let us find the sum. Sn is equal to N by 2 multiplied by 2A plus N minus 1D and we have to find S15 so substituting the value of A, DNN we get 15 by 2 multiplied by 2 into 8 plus 15 minus 1 multiplied by 8 which is equal to 15 by 2 multiplied by 16 plus 14 into 8 which is equal to 15 by 2 multiplied by 16 plus 112 which is equal to 15 by 2 multiplied by 128. Now 128 get cancelled by 2 so we get here 64 which is equal to 15 into 64 which is equal to 960. Therefore sum of first 15 multiples of 8 is 960 I hope you understood the question. Bye and have a nice day.