Hi,
I'd be happy to help here.
We are dealing with what is called a parallel circuit, which i think you already know. In a parallel circuit, the voltage is the same across every element, which i think you already know too. And the current splits, which i see you already know. This is different from a series circuit where the current is the same and the voltage is different across every element.
When we have to resistors in parallel we can calculate the "total resistance" RT by using the formula:
RT=R1*R2/(R1+R2)
or the equivalent formula:
RT=1/(1/R1+1/R2)
The first formula is a little nicer looking, but the second formula generalizes to more than two resistors so it is good to know too:
RT=1/(1/R1+1/R2+1/R3+...+1/Rn)
where Rn is the last resistor.
So what this means is we just have to take the reciprocal of each resistor and add them together, and then when we are done with all the additions we take the reciprocal of the final result and that gives us the total resistance.
So for example, say we have two resistors, R1=3 ohms, R2=6 ohms.
First we take the reciprocal of R1 and we get 1/3=0.33333333 aprpoximately.
Next we take the reciprocal of R2 and we get 1/6=0.16666666 approximately.
Now we add those two results together:
0.33333333+0.16666666
and we get:
0.5
Now last we take the reciprocal of that 0.5 and we get:
1/0.5=2 ohms
So the total resistance is 2 ohms.
If we had three resistors in parallel then we would do the same except then we would have three to add up before taking the last reciprocal.
Another way to state this is that we add up all the conductances, then take the reciprocal.
The conductance is simply the reciprocal of the resistance so for a 2 ohm resistor the conductance is 1/2=0.5 and that's about it.