Question

The first term of an AP is 1 and nth term is 25 if Sn = 520 then n=?

Answer 1

hope this answer will be helpful ^_^

Answer 2

n = 40

Step-by-step explanation:

Given,

The first term (a) = 1, $a_{n}$ = 25 and $S_n$ = 520

To find, the value of n = ?

We know that,

The sum of up to nth term of an AP

$S_n$ = $\dfrac{n}{2}(a+a_{n})$

∴ $\dfrac{n}{2}(1+25)$ = 520

⇒ $\dfrac{n}{2}(26)$ = 520

⇒ 13n = 520

Dividing both sides by 13, we get

$\dfrac{ 13n }{13}$= $\dfrac{520}{13}$

⇒ n = 40

∴ n = 40