1. The problem statement, all variables and given/known data The turns ratio of a transformer is 20:1 step down and the primary coil is connected to a 220V a.c. supply. If the secondary coil is connected to a '36W, 15V' light bulb and the efficiency of the transformer is 80%,find the current in the primary coil. 2. Relevant equations P=IV, Ns/Np=Ip/Is 3. The attempt at a solution I calculate by 36/0.8 = 45 W, 45/220 = 0.204A, which is the answer of D, but the correct answer is B, which is 0.11A, Am I wrong or the is the question wrong?