Question 42

Jambmaths question: 

Find the sum of the first 20 terms of the terms 8, 12, 16,-----,96

Option A: 

1040

Option B: 

960

Option C: 

920

Option D: 

1450

Jamb Maths Solution: 

$\begin{align}  & n=20,\text{ }a=8,\text{ }d=12-8=4 \\ & {{S}_{n}}=\tfrac{n}{2}\left[ 2a+(n-1)d \right] \\ & {{S}_{20}}=\tfrac{20}{2}\left[ 2\times 8+(20-1)4 \right] \\ & {{S}_{20}}=10\left[ 16+(19)4 \right]=10\left[ 16+76 \right] \\ & {{S}_{20}}=920 \\\end{align}$

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