Find the equivalent resistance between point $A$ and $B$ in the following circuit. (The resistance of each resistor is $R$ )

In a meter bridge the balancing length from the left end is found to be 25 cm . The value of the unknown resistance is (assume, standard resistance of $1 \Omega$ is in the right gap)

The resistance of a wire is $20 \Omega$. It is stretched, so that the length becomes three times, then the new resistance of the wire will be

In a meter bridge the resistances $R$ and $S$ are such that the null point is found at a distance of 40 cm from one end. If a resistance of $10 \Omega$ is connected in parallel with shunt $S$, then the null point occurs at 90 cm from the same end. The values of the two resistances $R$ and $S$ respectively are