Answer :
Final answer:
The effective resistance of a 25-ohm and a 15-ohm resistor in series placed in parallel with a 40-ohm resistor is 20 ohms, not any of the listed options.
Explanation:
To determine the effective resistance when resistors are in a series and parallel circuit, we first consider the resistors in series. In a series circuit, the resistances simply add up. So, the total resistance of a 25 ohm and 15 ohm in series is 25 + 15 = 40 ohms.
Now, this 40-ohm series circuit is in parallel with a 40-ohm resistor. The formula used to calculate the total resistance of two resistors in parallel is given by Reff = (R1 * R2) / (R1 + R2) = (40*40) / (40+40) = 1600/80 = 20 ohms.
So, the correct answer is not listed in the options you provided. The effective resistance of this combination is 20 ohms.
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