Which of the following is true for a parallel combination of two resistors?

Find the equivalent resistance of the following circuit.

What will be the equivalent resistance between points $A$ and $B$ of the following electric circuit?

How can three resistors of resistances $2 \,\Omega$,$3 \,\Omega$,and $6 \,\Omega$ be connected to give a total resistance of $4 \,\Omega$?

Three incandescent bulbs of $100\, W$ each are connected in series in an electric circuit. In another circuit,another set of three bulbs of the same wattage are connected in parallel to the same source. Now,if one bulb in both the circuits gets fused,will the rest of the bulbs continue to glow in each circuit? Give reasons.

$B_{1}$,$B_{2}$ and $B_{3}$ are three identical bulbs connected as shown in the figure. When all the three bulbs glow,a current of $3 \, A$ is recorded by the ammeter $A$.
$(i)$ What happens to the glow of the other two bulbs when the bulb $B_{1}$ gets fused?
$(ii)$ What happens to the reading of $A_{1}$,$A_{2}$,$A_{3}$ and $A$ when the bulb $B_{2}$ gets fused?