Question 25

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waecmaths question: 

A sequence is given 2 ½ , 5, 7½….. if the nth term is 25. Find n

Option A: 

9

Option B: 

10

Option C: 

12

Option D: 

15

waecmaths solution: 

$\begin{align}  & a=\frac{5}{2},\text{ }d=5-\frac{5}{2}=\frac{5}{2} \\ & {{T}_{n}}=a+(n-1)d \\ & 25=\frac{5}{2}+(n-1)\frac{5}{2} \\ & \frac{55}{2}=\frac{5}{2}(n-1) \\ & (n-1)=\frac{55}{2}\times \frac{2}{5} \\ & n-1=11 \\ & n=12 \\\end{align}$

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