physics (please check)

A total resistance of 3 ohms is to be producd by combining an unknown resistor R with a 12 ohm resistor. What is the value of R and how is it connected to the 12 ohm resistor
a) 4.0 ohm parallel
b) 4.0 ohm in series
c) 2.4 ohm in parallel
d) 2.4 in series
e) 9.0 in parallel

My work: A, 1/12 + 1/4= 1/3 or 3 ohm resistance

By using only two resistors, R1 and R2, a student is able to obtain resistance of 3 ohm, 4 ohm, 12 ohm, and 16 ohm using the alone combination. The values of R1 and R2 (in ohms) are:
A) 3,4
b) 2,12
c) 3, 16
d) 4, 12
e) 4, 16

My answer is d 4,12. Since 4 is alone, 12 is alone. in series 12+4=16 and in parallel the value is 3.

thank you


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  1. 12*R/(12+R) = 3
    3R + 36 = 12R.
    9R = 36.
    R = 4 Ohms in parallel.

    4, and 12 Ohms.

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    2. 👎

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    2. 👎
  3. D,4 ohm, series

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    2. 👎
  4. 4 ohm Parallel is correct.

    12+ 1/4 =3ohm
    => 4ohms parallel is correct

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