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Concept 2 of 9

Water Images: Top-Bottom Flip

1

Today's big idea

A water image swaps top and bottom, so letters symmetric that way survive.

Flipping 6 in water gives a backwards 9, not a plain one.

2

How it works

👀 What's going on?

A building reflected in still water comes back upside down, not back to front. That single difference decides every answer in this topic.

💡 Here's the trick

Water image flips top ↔ bottom6water66 flipped top-bottom = 90 and 8 unchanged · 6 ↔ 9 · each letter flips, order stays

Look at the pool above. A water image swaps top and bottom and leaves left and right where they were. A letter with a horizontal line of symmetry lands back on itself.

🪄 How to do it

  1. 1.Draw a horizontal line across each letter in the pool above.
  2. 2.Ask whether the top half matches the bottom half.
  3. 3.If they match the letter survives, and if not it flips.

✍️ Try it

Does C change in a water image? Then: does A?

C is symmetric top to bottom, so C looks the same. A is symmetric left to right instead, so A does change.

⚠️ Watch out

You might be thinking the water image of 6 is a 9. It is not. Flipping 6 top to bottom gives a 9 that is also back to front, because a water flip is a half turn plus a mirror. Only a plain half turn gives an ordinary 9.

🌟 Why this matters

Photographs of a lake at dawn show this every time, and knowing which way the flip runs tells you which shapes will look untouched.
Exam tip: B, C, D, E, H, I, O and X are the letters a water image leaves alone.

3

Watch me solve one

Quanta solves it

“Watch how I think through one of these — then you try.”

THE PROBLEM

“What is the water image of the capital letter M?”

  1. 1

    Water image = top-bottom flip

    Imagine reflecting M in a horizontal pond. 💧

  2. 2

    Mentally flip

    M has two points sticking up; flipped, they hang down and it reads W.

  3. 3

    Answer ✓

    W

Now you try one — same steps, different story 👇

4

See it in action

⚡ Time to play!

A pond reflects TOP ↔ BOTTOM. Reveal the reflection, then name it.

WATER IMAGE · ROUND 1 OF 3

b
💧 WATER?
5

Quick check

✅ VERIFICATION

Which of these letters is UNCHANGED in a water image?

⚡ Finish the activity above first to answer.

Keep going!

Up next: Embedded Figures

Count the units, then combine, then add the outer.

Concept 3 of 9 →