Question

Find the sum of 25 terms of arithmetic sequences of 11,22,33....

Answer 1

Sn = n/2 ( 2a+ n-1×d )
=> 25/2( 22+24×5)
=> 1775

Answer 2

Answer:

1775

Step-by-step explanation:

Hers, first term a =11

second term = 22

number of terms = n  = 25

so, common difference d = second term - first term

= 22 - 11 = 11

Now, sum on n terms = $S_{n}  = \frac{n}{2}  (2a +(n-1)d)$

or,  $S_{25}  = \frac{25}{2}  (2(11) +(25-1)11)$

$\frac{25}{2}  ((22 + (24)(11) ) = \frac{25}{2}  ((22 + 264 )\\\frac{25}{2}  (286 )  = \frac{286 \times 25}{2}$

or, $S_{25}   = 1775$