Question

PLLLZ HELP Find Sn if a1 = 20, d = –10, and n = 25.

Answer 1

Option A: $-2500$ is the value of $S_{25$

Explanation:

It is given that the first term is $a_1=20$

The common difference is $d=-10$

We need to determine the sum of 25 terms.

The sum of  terms of an arithmetic series can be determined using the formula, $S_n=\frac{n[2a_1+(n-1)d]}{2}$

Substituting $n=25$ , $a_1=20$ and $d=-10$

Thus, we have,

$S_{25}=\frac{25[2(20)+(25-1)(-10)]}{2}$

Simplifying the values, we get,

$S_{25}=\frac{25[40+(24)(-10)]}{2}$

$S_{25}=\frac{25[40-240]}{2}$

Subtracting the terms within the bracket, we get,

$S_{25}=\frac{25[-200]}{2}$

Multiplying the terms in the numerator, we have,

$S_{25}=\frac{-5000}{2}$

Dividing, we get,

$S_{25}=-2500$

Thus, the sum of the 25 terms is $-2500$

Therefore, Option A is the correct answer.

Answer 2

Answer:

-2500 answer

Step-by-step explanation: