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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