If in a mirror a clock shows the time as 11:20, then the real time is:

Concept: When a 12-hour analogue clock is viewed in a mirror, the reflection reverses the direction the hands appear to move. As a result, at any instant the real time and the time the mirror displays always add up to a constant total of 12:00, written as 11:60 in hours:minutes so it can be subtracted directly (since 60 minutes make 1 hour). So: Real time = 11:60 minus Mirror time.

1. Write the mirror-clock formula: Real time = 11:60 minus Mirror time.

2. Substitute the mirror reading (11:20) into the formula: Real time = 11:60 minus 11:20.

3. Subtract the hours and minutes separately: (11 minus 11) : (60 minus 20) = 0:40.

4. Convert 0:40 to standard 12-hour clock notation -- since 0 hours reads as 12 on a 12-hour dial, 0:40 is written as 12:40.

Cross-check: adding the real time and the mirror time should return the constant total -- 0:40 + 11:20 = 12:00, confirming the relationship holds. So the real time is 12:40.