Q45 of 84 Page 5

Find the sum :

 (CBSE 2013)


a = 18, d = - 18 =


Last term, an =


an = a+ (n – 1)d


= 18 + (n – 1) ()


-99 = 36 + 5 – 5n


-140 = -5n


n = 28


S28= [a + l]


= 14 (18 - )


= 7 (36 – 99)


= 7 (-63) = -441

More from this chapter

All 84 →
43

The nth term of an AP is given by (- 4n + 15). Find the sum of first 20 terms of this AP? (CBSE 2013)

 44

The sum of first n terms of an AP is 3n2+4n. Find the 25th term of this AP. (CBSE 2013)

 46

The sum of first n terms of an A.P. is . If its mth term is 168, find the value of m. Also, find the 20th term of this A.P. (CBSE 2013)

 47

The sum of first q terms of an A.P. is 63q – 3q2. If its pth term is-60, find the value of p. Also, find the 11th term of this A.P. (CBSE 2013)