Caesar Cipher — Shift Each Letter

Coded Language questions are one of the most satisfying types in OC Thinking Skills — once you understand the underlying rule, decoding the message becomes almost mechanical. Let's start with the most common and most teachable variant: the Caesar cipher, where every letter in the message was shifted forward by a fixed number of places.

Shift ciphers appear consistently across OC TS tests and are reliable marks for students who practise the technique. The rule is always the same: encoding shifts letters forward, so decoding shifts them back by the same amount. The only trap is the wrap-around near the end of the alphabet.

The examiner wants to confirm that you can reverse an encoding rule systematically. Given that letters were shifted +N places to encode, you must shift −N places to decode — and handle the alphabet wrap-around (e.g. D − 3 = A, C − 3 = Z) without losing track.

A ciphertext (a string of letters with no spaces) is given along with the shift amount. Spaces are removed before encoding, so you'll need to add them back by matching the decoded letters against the answer options. Sometimes two example words are given instead of the shift amount — you must deduce the shift by comparing them.