The sum of all natural numbers between $1$ and $100$ which are multiples of $3$ is
$1680$
$1683$
$1681$
$1682$
If $b + c,$ $c + a,$ $a + b$ are in $H.P.$, then $\frac{a}{{b + c}},\frac{b}{{c + a}},\frac{c}{{a + b}}$ are in
Find the sum of all numbers between $200$ and $400$ which are divisible by $7.$
If $\log 2,\;\log ({2^n} - 1)$ and $\log ({2^n} + 3)$ are in $A.P.$, then $n =$
If $\frac{a}{b},\frac{b}{c},\frac{c}{a}$ are in $H.P.$, then
Let ${\left( {1 - 2x + 3{x^2}} \right)^{10x}} = {a_0} + {a_1}x + {a_2}{x^2} + .....+{a_n}{x^n},{a_n} \ne 0$, then the arithmetic mean of $a_0,a_1,a_2,...a_n$ is