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Two resistors in series give an equivalent resistance s, and in parallel give an equivalent resistance p. If s = n*p, find the minimum possible value of n (rounded to the nearest integer).

1. 2
2. 3
3. 4
4. 5

Correct answer: 4

Solution

n = (R1 + R2)²/(R1*R2), which by AM-GM is minimized when R1 = R2, giving n = 4.

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