Letter codes：全部卡片

Its position in the alphabet, counting A as 1

提示A is 1, B is 2 — carry on the same way.

为什么B is 2, C is 3, all the way to Z at 26. Numbers decode back into letters the same way — and the worked pair in the question shows you the system before you use it.

How far each letter has shifted along the alphabet

提示Compare the worked pair — count the jump, then use that same jump on the new word.

为什么The move is fixed: if A becomes C, every letter goes two places forward. It can also run backwards, so check the direction from the example before you start.

Undo the shift, moving each letter back the same distance

提示Whatever the code did, do the reverse to return home.

为什么One worked pair fixes the shift. To encode, apply it; to decode, reverse it — two directions of the same rule.

The alphabet wraps round and carries on from A

提示Picture the letters written in a circle rather than a line.

为什么After Z comes A again, and before A comes Z — so a shift of two forward turns Y into A. Watch out: letter SEQUENCES are different, and never wrap.

5

提示Count up from A on your fingers — it is not far.

为什么E is a handy anchor: from it you can reach D or F in one step instead of counting from A every time.

10

提示The first letter to need double figures — a nice round number.

为什么J at ten is the anchor for the front of the alphabet: A to J is exactly ten letters, so anything nearby is one or two hops away.

20

提示J is ten — this one is twice as far along.

为什么E 5, J 10, T 20: with three anchors you rarely count more than a few letters in either direction.

26

提示The very last letter — how many letters are there altogether?

为什么Knowing the alphabet ends at 26 lets you count from the back: the 25th letter is Y and the 24th is X.

M and N

提示Thirteen letters on each side — the halfway pair.

为什么M is the 13th letter and N the 14th. Starting a count from the middle is often quicker than starting from A.

27

提示One more than the number of letters in the alphabet.

为什么C is the 3rd letter, and 27 − 3 = 24, so C is the 24th from the end. Mirror-code questions lean on this constantly.