Mirror & Water Images
🔒 Log in to trackMirror image of a clock
🔒 Log in to trackWhen a clock is seen in a vertical mirror, both hands swap sides of the 12–6 line. The time shown by the image and the actual time always add up to 12:00 (on a 12-hour clock).
So: image time = 11:60 − actual time (and actual = 11:60 − image, the same rule both ways). Writing 12:00 as 11:60 avoids borrowing.
Exception: if the actual time is 12:00 or 6:00, the image shows the same time. For times between 12:00 and 1:00 (like 12:20), use 23:60 − time (answer 11:40).
Water images of clocks usually put the hour hand in a position that no real time matches, so exams mostly ask about mirror images.
Detailed notes
Why the 11:60 rule works
A clock seen in a vertical mirror has its hands swapped across the 12–6 line. A hand 20 minutes past 12 on the right side appears 20 minutes before 12 on the left. So the actual time and the image time always add up to 12:00.
Writing 12:00 as 11:60 saves you from borrowing. The rule works both ways: actual = 11:60 − image.
Examples:
- 3:45 → 11:60 − 3:45 = 8:15
- 10:10 → 1:50
- 7:05 → 4:55
Special times
- 12:00 and 6:00 look the same in a mirror. These are the only two such times, because both hands then lie on the 12–6 line.
- Times between 12:00 and 1:00 (like 12:20): use 23:60 − time → 11:40. Or treat 12:20 as 0:20 and do 11:60 − 0:20 = 11:40.
- Whole hours: h:00 → (12 − h):00. So 4:00 → 8:00.
- With seconds: use 11:59:60 − time. So 2:25:40 → 9:34:20.
Reading a clock face in a mirror
When a figure shows a mirrored clock without numbers:
- The 12 mark is still at the top.
- Read the time the hands seem to show (the image time).
- Actual time = 11:60 − image time. A hand pointing to the 2 o'clock position in the image was really pointing to the 10 o'clock position.
Two-step questions
- "The mirror shows 4:20. What will the actual time be after 1 hour 15 minutes?" First find the actual time: 11:60 − 4:20 = 7:40. Then add: 7:40 + 1:15 = 8:55.
- Mirror of a mirror gives back the actual time.
Traps in the options
- 12:00 − time done wrongly: 12 − 3 = 9 and 60 − 45 = 15 gives 9:15 for 3:45. The hour must drop by one when the minutes are not zero, so the answer is 8:15.
- Half-turn time: 3:45 + 6:00 = 9:45 is where the hands are after a 180° turn, not a mirror image.
- Hours mirrored, minutes kept (8:45): only half the job.
Why the hour drops by one
Take 3:45. The hour hand is three-quarters of the way from 3 to 4. In the mirror it sits three-quarters of the way from 9 to 8, so it is past 8, not past 9. The image shows 8:15, not 9:15. Whenever the minutes are not zero, the image hour is 11 − h, not 12 − h.
Worked example
The mirror image of a clock shows 5:35. Find the actual time. Actual = 11:60 − 5:35 = 6:25. Check: 5:35 + 6:25 = 12:00. An option of 7:25 comes from forgetting to borrow; 11:35 is the half-turn time.
Check
Add your answer to the given time. The sum must be exactly 12:00 (or 24:00 for 12:xx times).
Quick revision
- Image = 11:60 − actual; actual = 11:60 − image.
- 12:xx → 23:60 − time; with seconds → 11:59:60 − time.
- 12:00 and 6:00 look unchanged.
- Mirrored clock face: read it as it looks, then take 11:60 minus that.
- Check: given + answer = 12:00.
Types of questions asked
Every way this subtopic shows up in exams — how to recognise it, the formula or logic to use, and a solved example.
Type 1: Mirror time from actual timevery common3 practice Q
A clock shows a time; what time does its mirror image show?
- Subtract from 11:60.
- Check that the sum is 12:00.
Why: each hand is reflected across the 12–6 line, so actual + image = 12 hours.
Example: A clock shows 3:45. What does its mirror image show?
11:60 − 3:45 = 8:15.
Type 2: Actual time from mirror readingcommon2 practice Q
The mirror image shows a time; find the actual time.
- Use the same rule: 11:60 − image time.
Why: reflecting twice gives back the original, so the rule works in both directions.
Example: A clock looks like 2:25 in a mirror. What is the actual time?
11:60 − 2:25 = 9:35.
Type 3: Special cases: 12:xx and secondsoccasional3 practice Q
Time between 12 and 1, a whole-hour time, or a time with seconds.
- 12:xx → 23:60 − time.
- Seconds → 11:59:60 − time.
- 12:00 and 6:00 map to themselves.
Why: the sum is still 12 hours; only the borrowing changes.
Example: What is the mirror image of 12:35?
23:60 − 12:35 = 11:25.
Type 4: Mirrored clock facecommon4 practice Q
A drawn clock (often without numbers) is said to be a mirror image; find the actual time.
- Read the time the hands appear to show.
- Actual = 11:60 − that time.
Why: reading the picture gives the image time; the rule converts it back.
Example: A mirrored clock face appears to show 2:30. What is the actual time?
11:60 − 2:30 = 9:30.
Type 5: Mirror time with elapsed timeoccasional3 practice Q
The mirror time is given and the question asks the actual time some minutes later (or earlier).
- Convert the mirror reading to the actual time first.
- Then add or subtract the elapsed time.
Why: time passes on the real clock; converting after adding gives a wrong answer.
Example: A mirror shows 4:20. What will the actual time be 1 hour 15 minutes later?
Actual 11:60 − 4:20 = 7:40; 7:40 + 1:15 = 8:55.
Formulas
Works in both directions; for 12:xx use 23:60 − T.
Shortcut tricks
⚡ 11:60 rule
Subtract the time from 11:60 digit-group-wise: hours from 11, minutes from 60.
Example: Q. A clock shows 4:20. What does its mirror image show?
Sol. 11:60 − 4:20 = 7:40.
Mirror time + actual time = 12:00.
Where students lose marks
Subtracting from 12:00 and mis-borrowing the minutes.
Applying the rule to 12:xx without adding 12 first.
Practice sets — 20 questions
Sets of 10, mixed across the question types above. Each answer comes with a step-by-step explanation.
Topic test · 10 questions
Suggested time 5 min · wrong answers go to your mistake notebook automatically.