Transformer dot prob don't understand (with sol)

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ssadi
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The problem:
Circuit schematic of a three-winding transformer with a 100 V source on the left, winding N1 with current I1, windings N2 and N3 with V2, I2, V3 and I3, a 10 ohm resistor and a 5 ohm load, and turns ratios N2/N1 = 1/2 and N3/N1 = 1.

Solution in the spoiler:
Worked solution to a coupled-coil problem listing V1 = 100 V, N2/N1 = 1/2, N3/N1 = 1, Z2 = 5 ohm, Z3 = 10 ohm, with parts (a) dot placement and (b)-(c) voltage and current calculations.

I don't know how to do the problem (a), but I also don't understand the answer (top of coil 3?). Can you give me the process on how to do the problem (a), i.e. in general how do I assign dots to coils in circuits? :)
 
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  • Worked solution for a transformer problem with three coils: parameters V1 = 100∠0° V, N2/N1 = 1/over 2, Z2 = 5 Ω, Z3 = 10 Ω; part (a) about dot placement, and part (b) and (c) calculations with phasor currents and voltages.
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  • Circuit schematic of a three-winding transformer with a 100 V source on the primary winding N1, a 5 ohm load on winding N2, and winding N3 feeding a 10 ohm resistor with voltage V3 and current I3.
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ssadi said:
The problem:
Circuit schematic of a three-winding transformer with a 100 V source on coil 1, a 5 ohm load on coil 2, a 10 ohm resistor on coil 3, and turns ratios N2/N1 = 1/2 and N3/N1 = 1 labelled.

Solution in the spoiler:
Worked solution to a coupled-coil transformer problem: V1 = 100 angle 0 V, N2/N1 = 1/2, Z2 = 5 ohm, Z3 = 10 ohm, with dot-placement conditions and step-by-step equations for V2, V3, I2, I3 and the MMF balance N1 I1 = N2 I2 + N3 I3.

I don't know how to do the problem (a), but I also don't understand the answer (top of coil 3?). Can you give me the process on how to do the problem (a), i.e. in general how do I assign dots to coils in circuits? :)

the answer was wrong, it should be right side for coil 3, after finding that out i understand.
 
Assume that the conductor enters the core from the back and exits the core from the front.
Put a dot where the conductor exits the core.
On the left hand coil the conductor exits the core on the top. (It enters the core on the bottom.
On the right hand coil the conductor exits the core on the top. Put a dot at the top of the right hand coil.
On the bottom coil the conductor exits the core on the right. Put a dot to the right of the bottom coil.