Two resistors of and are connected in parallel. What is the equivalent resistance (in )?

Answer and explanation

Correct answer: D. 4

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  1. Step 1: In a parallel combination of two resistors, equivalent resistance satisfies .
  2. Step 2: Insert and : .
  3. Step 3: Simplifying the fraction gives .
Answer
4.
Why not the others: '25' adds the resistances in series () rather than parallel; '15' adds rather than subtracts the constant term in the final step in evaluating ; '25/2' takes the arithmetic mean of the two resistors rather than reciprocal sum.

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