Effective Resistance of a circuit

[logearav]

Homework Statement

Revered members,
I need to find the effective resistance of this circuit which i have given in attachment.
circuit.

Homework Equations

The Attempt at a Solution

Now let me explain how i carried out.
I proceeded from right to left
1) R s = 12 + 6 = 18Ω
2) Rp = R1 R2/R1 + R2 which is (18 x 6)/24 = 4.5Ω
3) R = R1 + R2 = 18 + 4.5 = 22.5Ω
I have given the above steps in my second attachment
Now, for the same problem when i proceed from left to right
1) I took 18Ω and 6Ω as parallel i got 4.5 Ω and then this 4.5 is in series with
12 Ω and 6Ω so 4.5 + 12 + 6 = 22.5Ω
I have given the above steps in my third attachment
Now my question is why should not i take 18 Ω and 6Ω as series connection and proceed, because when i take those 18 Ω and 6Ω as described in my last attachment in the following reply,
i get wrong answer. Where do i go wrong?

Homework Statement

Homework Equations

The Attempt at a Solution

 

[logearav]

continuing my previous query, this is my last attachment. Is this not a series circuit? But when i take this as series and proceed from left to right, i get wrong answer.

 

[lewando]

why should not i take 18 Ω and 6Ω as series connection and proceed?

Because, in the first image, they are not in series. You were correct in proceeding from right to left (2nd image).