Answer:
Saturday.
Explanation:
To answer the above question, we must recognise that Tuesday appears once every 7 days.
If today is Tuesday, 31 days ago will be obtained as follow:
31/7 = 4 remainder 3
Thus
31 = (7 × 4) + 3
31 = (28) + 3
Thus, the 28th day is Tuesday. If we count 3 days back from Tuesday, the day will be Saturday.
Therefore, the magician made his wife disappear on Saturday.