suppose you have 3 resistors, each of value 0f 30 omega. List all the different resistances that you can obtain by combining them
write 30 ohms or 30Ω, don't write the name of the Greek letter.
3 in series: 90Ω
2 in series, in parallel with 1: 20Ω
1 in series with 2 in parallel: 45Ω
3 in parallel: 10Ω