Question 20

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Jambmaths question: 

The fifth term of AP is 24, and eleventh term is 96. Find the first term

Option A: 

12

Option B: 

4

Option C: 

-12

Option D: 

-24

Jamb Maths Solution: 

$\begin{align}  & {{T}_{n}}=a+(n-1)d \\ & {{T}_{5}}=a+4d=24----(i) \\ & {{T}_{11}}=a+10d=96---(ii)\, \\ & \text{Solving equation }(i)\text{ and }(ii) \\ & 6d=72 \\ & d=\frac{72}{6}=12 \\ & \text{Substituting }12\,\text{for }d\text{ in }(i) \\ & {{T}_{5}}=a+4(12)=24 \\ & a=24-48 \\ & a=-24 \\\end{align}$

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