80 answers
Np/Ns = Vp/Vs =Turns ratio
Where; Np is the number of turns in the primary coil, Ns is the number of turns in the secondary coil, Vp is the voltage in the primary coil, Vs is the voltage in the secondary coil.
40/Ns = 80/160
40/Ns = 1/2
Ns = 80 turns