 Now that we've developed these new rules for adding resistors that are in series or in parallel, let's apply it to a circuit. So if you have a look here, I've created a circuit which has got once again our 9-volt battery, and then it's got three resistors. Now if you look very carefully, we've actually got one resistor which is connected directly to the negative terminal. Then there's two resistors which are both connected to the first resistor and both connected to the positive terminal. So what this means is that these two resistors are in parallel with each other and together they are in series with this resistor here. So let's draw a circuit diagram of what this looks like. So here is my circuit diagram and what I'd like to figure out is what is the total effective resistance of all three resistors and also how much current would flow through this circuit. So when it comes to circuits, the best way to solve them is using divide and conquer. So I'm going to start out by looking at the resistors in parallel. So let's look at this section here. So I'm going to call the total resistance of these two resistors RP, which stands for resistance parallel, but you could call it anything you wanted to. And using the formula for resistance in parallel, I get this is equal to 1 over RP equals 1 over 1 ohm plus 1 over 1 ohm. So in this case, 1 divided by 1 is simply 1 and this one divided by 1 is also simply 1. So I can just do this is 1 plus 1 and so that's going to give me 2. So 1 over RP is equal to 2 and the units use inverse ohms. So that means if I was to flip both sides of the equation that I would get, the RP is equal to a half an ohm, which is equal to 0.5 ohms. So I figured out this first bit that I've highlighted in yellow. So to figure out the total resistance, then I'll need to add this yellow bit to the one ohm resistor. Since these two sections are in series, I can use the series resistance formula. So in this case, I'm going to call the total resistance of all of this RT for R total and it's equal to half an ohm plus one ohm, which equals 1.5 ohms. So I figured out the total resistance of the whole circuit. If I want to figure out the current, what I need to do is then use ohms law. And in this case, I get nine volts divided by 1.5 ohms, which gives me six amps. There we go. We calculated the total resistance and the current in the circuit.