Question

Under the tree plantation scheme Mr. Sunil planted $1$ tree on the first day, $2$ trees on the second day, $3$ trees on the third day and so on. What will be the total number of trees planted after $10$ days?

Answer 1

Trees planted by Mr. Sunil are $1$, $2$, $3$,....
Here, $t_1=1$, $n=10$
Therefore, $t_n=t_{10}=10$; $S_n=S_{10}=$?
$\Rightarrow S_n=\frac{n}{2}(t_1+t_n)$
$\Rightarrow S_{10}=\frac{10}{2}(1+10)$
$\Rightarrow S_{10}=\frac{10}{2}\times 11=55$
Hence, total number of trees planted after $10$ days will be $55$.