Q29 of 89 Page 51

Find the sum of all the 11 terms of an AP whose middle most term is 30.

No of terms = 11 as it is even

Middle term will be i.e. 6^th term

Let the first term be a and common difference be d of an AP

a_n = a + (n - 1)d

a₆ = a + (6 - 1)d

30 = a + 5d [ eqn 1]

Now as we know,

[ using eqn 1]

Find the sum of first 17 terms of an AP whose 4th and 9th terms are - 15 and - 30, respectively.

If sum of first 6 terms of an AP is 36 and that of the first 16 terms is 256, then find the sum of first 10 terms.

Find the sum of last ten terms of the AP 8, 10, 12, …, 126.

Find the sum of first seven numbers which are multiples of 2 as well as of 9.