Solve:

25 + 22 + 19 + 16 + … + x = 115

given is an AP whose first term a is 25 and d is - 3(22 - 25) with a number of terms equal to..

To find: the value of x for the given AP

Now for the finding number of terms, the formula is

Hence the sum is given by the formula

Now substituting the values in the above formula

It is given that s = 115, so equating the above expression to 115

Solving we get n is 10 or

Since n cannot be a fraction, so we choose n as 10

x = - 2