If three resistors of $5 \Omega$,$10 \Omega$,and $15 \Omega$ are connected in series,the equivalent resistance $R$ is equal to ........ (in $\Omega$)

Calculate the equivalent resistance in the combination shown in the figure below.

In a circuit containing two unequal resistors connected in parallel:

Two wires of the same metal have the same length, but cross-sections are in the ratio $3 : 1$. They are joined in series. The resistance of the thicker wire is $10\, \Omega$. The total resistance of the combination will be:

In the figure given below,$A, B$,and $C$ are three ammeters. The ammeter $B$ reads $0.5\, A$. (All the ammeters have negligible resistance.) Calculate:
$(i)$ the readings in the ammeters $A$ and $C$.
$(ii)$ the total resistance of the circuit.

Three resistors of $5 \, \Omega$,$10 \, \Omega$,and $15 \, \Omega$ are connected in series,and the combination is connected to a battery of $30 \, V$. An ammeter and a voltmeter are connected in the circuit. Draw a circuit diagram to connect all the devices in the correct order. What is the current flowing through the circuit and the potential difference across the $10 \, \Omega$ resistor?