Two 20 ohm resistors are connected in parallel and two 10 ohm resistors are connected in parallel. if these two combinations are connected in series the equivalent resistance of the combination is: a) 20 ohm b) 10 ohm c) 15 ohm d) 30 ohm

C. 15Ω.

The circuit diagram is shown in the first image attached. To solve this problem we have to use the equivalent resistor conected in parallel Req = (R1*R2)/(R1+R2).

Calculating the equivalent resistor in the 20Ω resistor parallel arrangement:

RAeq = [(20*20)/(20+20)] Ω

RAeq = 400/40 Ω

RAeq = 10Ω

Calculating the equivalent resistor in the 10Ω resistor parallel arrangement:

RBeq = [(10*10)/(10+10)]Ω

RBeq = 100/20 Ω

RBeq = 5Ω

Both equivalent resistors are in series. So, in order to calculate the equivalent resistance of the combination:

Rtotal = RAeq + RBeq

Rtotal = 10Ω + 5Ω

Rtotal = 15Ω

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