Question

1: Find the number of terms, n, of the arithmetic series given

Answer 1

Given,

The first term of the series is 21.

The last term of the series is 39.

The sum of the series is 210.

Required

The number of terms in the series.

The sum of the series is calculated as,

`S=(n)/(2)(a+a_n)`

Substituting the values then,

`\begin{gathered} 210=(n)/(2)(21+39) \\ 420=n(60) \\ n=7 \end{gathered}`

Hence, the number of terms in the series is 7.