Primary has 100 turns.
Secondary #1 has 50 turns and a 10 ohm impedance.
Secondary #2 has 25 turns and an impedance of 25 ohm.
What is the primary impedance. I know the answer but don't know how it was derived. Any help would be appreciated.

 

I think you calculate the primary impedance from each secondary (using the turns ratio) and then parallel the two values on the primary side. I can't remember if the impedance reflects back using the turns ratio or the turns ratio squared? I suspect the latter.

Is the answer about 36?

 

Use impedance matching to match the impedance on secondary #2 to secondary #1. Combine the two impedances and match that impedance to the primary winding.

Impedance matching is related to the square of the two turns ratio through which you are matching.

 

The formula that my textbook taught number of windings primary/by number of secondary, square the answer and x the secondary impedance so my answer was coming up 62 ohms. Bounty Hunter, your answer is correct.

 

Got it, thanks guys.

 

The formula that my textbook taught number of windings primary/by number of secondary, square the answer and x the secondary impedance so my answer was coming up 62 ohms. Bounty Hunter, your answer is correct.

You should understand that the formula you mentioned above is only valid if your are matching impedances to the primary winding.