Question 22

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Jambmaths question: 

The sum of the first term of an arithmetic progression is 252, if the first term is –16 and the last term is 72. Find the number of terms in the series.

Option A: 

6

Option B: 

7

Option C: 

8

Option D: 

9

Jamb Maths Solution: 

$\begin{align}  & {{S}_{n}}=252 \\ & a=-16 \\ & {{T}_{n}}=l=72 \\ & {{S}_{n}}=\tfrac{n}{2}\left[ a+l \right] \\ & 252=\tfrac{n}{2}\left[ -16+72 \right] \\ & 252=\tfrac{n}{2}\left[ 56 \right] \\ & 252=28n \\ & n=9 \end{align}$

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