65
Find the common difference of an A.P. whose first term is $8$, the last term is $65$ and the sum of all its terms is $730$.
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$a = 8, l = 65$
$$\begin{aligned}& 730 = \frac{n}{2}[8+65] \\ & n = \frac{730 \times 2}{73} = 20\end{aligned}$$
$$\begin{aligned}& \therefore l = a + 19d \implies 65 = 8 + 19d \\ & \implies d = 3\end{aligned}$$
$$\begin{aligned}& 730 = \frac{n}{2}[8+65] \\ & n = \frac{730 \times 2}{73} = 20\end{aligned}$$
$$\begin{aligned}& \therefore l = a + 19d \implies 65 = 8 + 19d \\ & \implies d = 3\end{aligned}$$