Series resistor calculator
Resistors in series simply add: R = R₁ + R₂ + … A 220, 330 and 470 ohm chain totals 1,020 ohms. The same current flows through every resistor, and the voltage divides between them in proportion to their values.
How to use a series resistor
A series resistor is the standard way to drop voltage or limit current, and its value follows from Ohm’s law on the difference. If a 5 V supply feeds something that wants 3.3 V at 20 mA, the resistor has to drop 1.7 V at 20 mA, which is 85 Ω. The catch is that the drop depends on the current: change the load and the voltage changes with it. That is why a series dropper is fine for an LED, whose current you control deliberately, and unsuitable for a circuit whose consumption varies.
Questions
Just add the values. Three resistors of 220, 330 and 470 ohms total 1,020 ohms.
Yes, in a series chain there is nowhere else for it to go. The voltage divides instead.
Divide the voltage you need to drop by the current the load draws. Then check the dissipation.
The largest, because it drops the most voltage at the same current.
It averages out somewhat across a chain, but the worst case is still the sum of the individual worst cases.