Using meter bridge, it is advised to obtain the null point in the middle of the wire. why?

In a meter bridge experiment null point is obtained at 20 cm. from one end of the wire when resistance X is balanced against another resistance Y. If XltY, then where will be the new position of the null point from the same end, if one deicdes to balance a resistance of 4 X against Y?

In a meter bridge the point D is a neutral point (Fig. EP 3.11)

Two parallel resistors of 5 ohm nd 20 ohm are connected in left arm of a metre bridge. If the null point is at 40 cm from left end of the wire, calculate the value of resistance connected in right arm.

Two resistances are connected in the two gaps of a meter bridge. The balance point is 20 cm from the zero end. When a resistance 15 Omega is connected in series with the smaller of two resistance, the null point shifts to 40 cm. The smaller of the two resistance has the value.

With the help of a circuit diagram, explain how a metre bridge is used to find the unknown resistance of a given wire.

Sometmes balance point may not be obtained on the potentiometer wire. Why?