science
posted by teresa .
There are three sources of resistance in a parallel circuit. Two of them are rated at 20 ohms, the other at 10 ohms. What is the circuits total resistance?

I assume all three are in parallel
first combine the two 20 ohms
1/R = 1/20 + 1/20 = 1/10
Req = 10
now combine that 10 with the other 10
1/R = 1/10+1/10 = 2/10 = 1/5
so R = 5 Ohms in the end