Find the sum of an $AP$ of $40$ terms whose first and last terms are $80$ and $275$.

The number $111...1$ ($91$ times) is a:

$A$ $G.P.$ consists of an even number of terms. If the sum of all the terms is $5$ times the sum of the terms occupying odd places,then the common ratio will be equal to

The sum of the series $\frac{1}{2} + \frac{1}{3} + \frac{1}{6} + \dots$ to $9$ terms is

If $\frac{a + bx}{a - bx} = \frac{b + cx}{b - cx} = \frac{c + dx}{c - dx}, (x \ne 0)$,then $a, b, c, d$ are in

In a geometric progression consisting of positive terms,each term is equal to the sum of the next two terms. Then the common ratio of the progression is equal to: