Engineering Electrical circuit porblem using ohms law

[babic]

Homework Statement

Using all the following resistors : 2 x 12 ohms , 2 x 24 ohms , and 2 x 36 ohms. create a circuit where the total resistance will be 4 ohms.

The problem states that I have to use ALL of the resistors..making it so complicated

Homework Equations

1/Req = 1/R1 + 1/R2 + 1/R3... (in parallel)
Req + R1+R2+R3... (in series)

The Attempt at a Solution

The closest I got was (1/12) + (1/(24+36)) + (1/36) + (1/12) + (1/24). Is there a trick or something..

I could have 4 parallel resistors.. 12 parallel to 12 parallel to 24 parallel to 24.
(1/24) + (1/24) + (1/12) + (1/12) = 1/4 ... but I did not use the 2 x 36 ohms.. help will be appreciated.

 

[Simon Bridge]

Welcome to PF;
I don't think there's a trick exactly - beyond understanding the problem.
i.e. since all the resistors are greater than 4ohms, you will need to combine a lot in parallel to reduce the overall resistance.

Also 12, 24, and 36, are all multiples of 4... your target resistance.

I guess you could design the circuit with a short circuit across unwanted resistors... but that is usually considered the same as not using them.

 

[phinds]

Hm ... I tried a few combinations and I can't get it either. My attempts were hardly exhaustive, but I sure don't see it.

 

[Simon Bridge]

3.9560Ω (the closest so far) is 4.0Ω rounded :)

Then there is the 12s and 24s in parallel, in series with the 36's in parallel - but short-curcuit the 36s :)

Since all values divided by 3 as well as 4 I figured looking at triples.
12 = 4x3x1
24 = 4x3x2
36 = 4x3x3

Then there is just trying every possible combination of series and parallel.
I don't think there would be more than two series sections... there won't be that many combinations.

 

[babic]

Thank you guys, I'll just stick with the 3.9560ohms answer.