If two resistors of 25 Ω and 15 Ω are joined together in series and then placed in parallel with a 40 Ω resistor, the effective resistance of the combination is :
(a) 0.1 Ω
(b) 10 Ω
(c) 20 Ω
(d)40 Ω
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Solution
(c) 20 Ω When 25 Ω and 15 Ω are connected in series, then: Total resistance, R = 25 + 15 = 40 ÃŽ This 40 ÃŽ is connected in parallel with the 40 ÃŽ resistor. Therefore, the net resistance = 40 / 2 = 20 ÃŽ