Question
In an AP: a = 3, n = 8, s = 192, find d.
✓
Answer
Here, a = 3
n = 8
S = 192
We know that
$S = \frac{n}{2}[2a + (n - 1)d]$
$ \Rightarrow 192 = \frac{8}{2}\left[ {2(3) + (8 - 1)d} \right]$
$ \Rightarrow 192 = 4[6 + 7d]$
$ \Rightarrow \frac{{192}}{4} = 6 + 7d$
$ \Rightarrow $ 48 = 6 + 7d
$ \Rightarrow $ 48 - 6 = 7d
$ \Rightarrow $ 42 = 7d
$ \Rightarrow $ 7d = 42
$ \Rightarrow d = \frac{{42}}{7}$
$ \Rightarrow $ d = 6
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