Two resistors are in the ratio $1:4$. If these are connected in parallel their total resistance becomes $20 \mathrm{\Omega }$. Find the value of each resistance.

Five resistors are connected as shown in Fig. Find the equivalent resistance between points $B$ and $C$.

If the reading of the ammeter $A_1$ in Fig. is $2.4 \mathrm{A}$, what will the ammeters $A_2$ and $A_3$ read? Neglect the resistances of the ammeters.

The resistance of the rheostat shown in Fig. is $30 \mathrm{\Omega }$. Neglecting the meter resistance, find the minimum and maximum current through the ammeter as the resistance of the rheostat is varied.

Find the current through the $5 \mathrm{\Omega }$ resistor in the circuit shown in Fig, when the switch $S$ is open.

Find the current through the $5 \mathrm{\Omega }$ resistor in the circuit shown in Fig, when the switch $S$ is closed.

Calculate the equivalent resistance between points $A$ and $B$ in each of the following networks of resistors: