The sum of first $n$ natural numbers is
$n\,(n - 1)$
$\frac{{n\,(n - 1)}}{2}$
$n\,(n + 1)$
$\frac{{n\,(n + 1)}}{2}$
The sum of all natural numbers between $1$ and $100$ which are multiples of $3$ is
A man deposited $Rs$ $10000$ in a bank at the rate of $5 \%$ simple interest annually. Find the amount in $15^{\text {th }}$ year since he deposited the amount and also calculate the total amount after $20$ years.
Let $S_{n}$ be the sum of the first $n$ terms of an arithmetic progression. If $S_{3 n}=3 S_{2 n}$, then the value of $\frac{S_{4 n}}{S_{2 n}}$ is:
If three numbers be in $G.P.$, then their logarithms will be in
Different $A.P.$'s are constructed with the first term $100$,the last term $199$,And integral common differences. The sum of the common differences of all such, $A.P$'s having at least $3$ terms and at most $33$ terms is.