Coding-Decoding: Secret Letter Shifts

Today's big idea

Find the shift between one letter pair, then apply it to the whole word.

Whatever jump one letter makes, every other letter makes the same jump.

How it works

👀 What's going on?

In a coding puzzle every letter slides the same distance along the alphabet. Work out how far it slid and the entire message opens up at once.

💡 Here's the trick

Look at the code above. Each letter has slid the same number of places along the alphabet; that slide is called the shift. Here every letter moves one place, so A becomes B and C becomes D. Find the shift from one pair you can already see, check it on a second pair, then slide backwards by that amount to decode.

🪄 How to do it

1.Compare one known letter pair to find the shift, as the picture above finds +1.
2.Check that the same shift works on a second pair.
3.Slide backwards by that amount to decode, wrapping past Z round to A.

✍️ Try it

CAT is coded as ECV. What is the shift, and what does the code word FGP mean?

C becomes E, which is a shift of +2, and A to C and T to V both agree. To decode FGP, slide each letter back 2: F becomes D, G becomes E, and P becomes N, giving DEN.

⚠️ Watch out

You might be thinking a letter near the end of the alphabet has nowhere left to go. It wraps around. Shifting Y forward by 2 passes Z and lands on A, and shifting B back by 3 lands on Y.

🌟 Why this matters

Secret messages between friends, the codes in adventure stories and the ciphers armies once used all work exactly this way. One shift unlocks every word written in it.
Exam tip: Always test your shift on a second letter pair, because a single pair can agree by luck.

Watch me solve one

Quanta solves it

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

THE PROBLEM

“If APPLE is coded as CRRNG, what is the shift?”

1
Compare one pair
A → C : 2 letters forward.
2
Verify with others
P → R: +2 ✓. L → N: +2 ✓. E → G: +2 ✓.
3
Shift confirmed
+2
4
Answer ✓
Shift = +2

Now you try one — same steps, different story 👇

See it in action

⚡ Time to play!

The code shifts each letter by +1. To decode, shift BACK by 1.

CIPHER · ROUND 1 OF 3

Shift rule: each letter moves +1 forward in the alphabet

A→B, B→C, C→D, ...

Coded Word

E↓?

P↓?

H↓?

Your turn: what does E − 1 decode to?

Quick check

✅ VERIFICATION

In a code, DOG becomes FQI. What does the code word JCV mean?

⚡ Finish the activity above first to answer.

Keep going!

Up next: Symbol Equations

Solve one shape first, then substitute it into the others.

Concept 3 of 7 →