Chapter 8.2, Problem 64E

To calculate: The ${100}^{th}$ partial sum of the arithmetic sequence.

To determine

The ${100}^{th}$ partial sum of the arithmetic sequenceis $16100$ .

Given information:

The given sequence has $a_1=15,a_{25}=307$

Definition used:

The nth term of the arithmetic sequence has the form $a_n=a_1+\left(n-1\right)d$ ,where $a_1$ is the first term of the sequence, and d is the common difference.

The sum of finite arithmetic sequence is given by $S_n=\frac{n\left(a_1+a_n\right)}{2}$ .

Here n is the number of terms, $a_1$ is the first term of the sequence, and $a_n$ is the last terms of sequence.

Calculation:

It is given that $a_1=15,a_{25}=307$ .

Compute the 100^th partial sum as follows,

  $\begin{array}{c}{S}_{100}=\frac{100\left(15+307\right)}{2}\\ =50\cdot 322\\ =16100\end{array}$

Therefore, the sum of the partial arithmetic sequence is $16100$ .

Answer to Problem 64E

The ${100}^{th}$ partial sum of the arithmetic sequenceis $16100$ .

Explanation of Solution

Given information:

The given sequence has $a_1=15,a_{25}=307$

Definition used:

The nth term of the arithmetic sequence has the form $a_n=a_1+\left(n-1\right)d$ ,where $a_1$ is the first term of the sequence, and d is the common difference.

The sum of finite arithmetic sequence is given by $S_n=\frac{n\left(a_1+a_n\right)}{2}$ .

Here n is the number of terms, $a_1$ is the first term of the sequence, and $a_n$ is the last terms of sequence.

Calculation:

It is given that $a_1=15,a_{25}=307$ .

Compute the 100^th partial sum as follows,

  $\begin{array}{c}{S}_{100}=\frac{100\left(15+307\right)}{2}\\ =50\cdot 322\\ =16100\end{array}$

Therefore, the sum of the partial arithmetic sequence is $16100$ .