A battery connected to a resistor supplies a current of 4 amps. If another resistor of equal resistance is connected in series with first resistor the current the battery supplies will be how much?

Half that, or 2 amps. The basic rule in circuits is that voltage (E) equals current (I) times resistance (R). Here's how that expression of Ohm's law looks: E= I x R That means that current equals voltage divided by resistance, as is shown here: I = E / R This expression says that resistance is inversely proportional to current (with voltage staying the same). Further, if resistance goes up, current goes down. If resistance doubles (goes up by a factor of 2), which it does in the case specified in the question, then current is cut in half (goes down by a factor of 2). Half of 4 amps is 2 amps, and that's where the answer came from.