$n$ equal resistors are first connected in series and then connected in parallel. What is the ratio of the maximum to the minimum resistance?

$A$ wire of resistance $9 \ \Omega$ is bent to form an equilateral triangle. Then the equivalent resistance across any two vertices will be . . . . . . ohm.

$10$ resistors,each of resistance $R$,are connected in series to a battery of $emf$ $E$ and negligible internal resistance. When those are connected in parallel to the same battery,the current is increased $n$ times. The value of $n$ is:

$A$ current of $15\,mA$ flows in the circuit as shown in the figure. The value of the potential difference between the points $A$ and $B$ will be $...\,V$.

Obtain the expression for the equivalent resistance for $3$ resistors connected in parallel and also write the expression of equivalent resistance for connection of $n$ resistors.

Four wires $AB, BC, CD, DA$ of resistance $4\, \Omega$ each and a fifth wire $BD$ of resistance $8\, \Omega$ are joined to form a rectangle $ABCD$,where $BD$ is a diagonal. The effective resistance between the points $A$ and $B$ is: