Question

If 26th term of an A.P is 150 find S51

Answer 1

T26 = a+25d
150 = a+25d

S51 = n/2 [2a+(n-1)d]
= (51/2) [2a+50d]
= 51 × (a+25d)
= 51×150
S51 = 7650

Answer 2

Let 'a' be the first term and common difference 'd'

T26 = a + 25d

S51 = n/2 [ 2a + (n - 1)d]
S51 = 51/2 [ 2a + (51 - 1)d]
S51 = 51/2 [ 2a + 50d]
S51 = 51/2 x 2( a + 25d)
S51 = 51 ( a + 25d)
S51 = 51 x 150
S51 = 7650