Question

What is the total resistance in a parallel circuit with a 10 ohm lamp and a 15 ohm lamp?

Answer 1

There is a formula you can use, but instead, do this:

assume 150 volts>
Current in 10 ohm resistor= 15a
current in 15 ohm reistor= 10 a

Net resistance= V/I= 150/25=6 ohms

and of course, you can do it the geek way:

1/Rtotal= 1/10 + 1/15

1/Rtotal= (15+10)/150= 1/6
Rtotal= 6 ohms.