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August 23, 2014

August 23, 2014

Posted by **Lizette** on Friday, October 12, 2007 at 1:50am.

- science -
**chanell**, Friday, October 12, 2007 at 4:18amletter B

- science -
**Dr Russ**, Friday, October 12, 2007 at 8:26amYou haven't stated the third resistance, but both A) and B) are not possible for any value in parallel with two 20 ohm resistors. The only possible answers are C) and D).

using 1/R(total) = 1/R +1/R +1/R

1/20 +1/20 =0.1

if the unstated value =x

A)

so 0.1 +1/x = 1/20 = 0.05

which requires a -ve value for x

B)

so 0.1 + 1/x = 1/12 = 0.0833

which requires a -ve value for x

C)

so 0.1 + 1/x = 1/8 = 0.125

which requires a value for x=40 ohms

D)

so 0.1 + 1/x = 1/5 = 0.2

which requires a value for x=10 ohms

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