Detective Agency
Detective agency: three cases, an evidence board and the final deduction
- Reordering Words
- Explore the Facts
3 cases · about 5 min
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11+ Verbal ReasoningFree to play · no sign-up
Codebreaker HQ: a free letter and number codes game for the 11+
Crack intercepted messages at a spy agency’s cipher machine and decrypt the secret message. Each right answer locks the rotors and lights up a letter of the message, and three in a row earns a Master Key with bonus letters and points.
No account needed. Badges and personal bests save in this browser.
A round16 intercepts · about 4 min
LevelsRecruit · Agent · Spymaster
Daily challengeA new challenge every day
Unlock: Arctic StationReach Spymaster rank to unlock
About Codebreaker HQ
Codebreaker HQ turns 11+ letter and number codes into a spy mission. A round is 16 intercepts in four missions of four, from London HQ to Berlin, Cairo, Tokyo and Rio, mixing letter codes, letter analogies, letter-word codes and number-word codes. The last intercept of each mission is a double agent: a harder question with ten extra seconds and 150 bonus points. At the end the secret message is typed out as a telegram.
It is free to play, with no sign-up: the whole game, all three levels and the daily challenge. A wrong answer sounds the alarm and the trap is explained, and no question ever times out. The mission debrief goes through every trap with a worked answer. Badges and personal bests are saved in this browser on this device, and reaching Spymaster unlocks the Arctic Station, with a new machine and four new cities.
How to play Codebreaker HQ
- Choose your clearance: Recruit, Agent or Spymaster.
- Read each intercept and tap the answer that cracks it, while the signal is strong for a speed bonus.
- Crack three in a row for a Master Key: two bonus letters and 100 extra points.
- Catch the double agent at the end of each mission for 150 bonus points.
- Read the mission debrief to see how each trap works, then start a new mission.
What it practises for the 11+
- Letter Codes
- Each letter of a word moves the same number of places along the alphabet to make a code, and your child finds the move and uses it. For example, if CAT is written DBU, each letter moves one place on, so DOG is EPH. Learn the topic →
- Letter Analogies
- Two pairs of letters are linked by the same move, and your child applies it to a new pair. For example, AB is to CD as PQ is to RS, because each letter moves two places on. Learn the topic →
- Letter-Word Codes
- A whole word is written in code, and your child works out the rule from an example to code a new word or turn a code back into a real word. For example, if MAN is written NBO, the code GJTI stands for FISH. Learn the topic →
- Number-Word Codes
- Letters stand for numbers, either their place in the alphabet (A = 1, B = 2) or a digit worked out from a word and its code. For example, if TEA is written 572, then EAT is 725. Learn the topic →
Letter codes, letter pairs and number codes are three of GL Assessment’s 21 verbal reasoning question types, and verbal reasoning is also set by CEM, ISEB and many independent schools (FSCE and CSSE set no reasoning papers).
Try Codebreaker HQ questions
Questions from the game, for you to try together. Have a go before opening the answer.
Question 1 · Letter Codes
Which code is right? If “CAT” is written as “FDW”, what is the code for “WIG”?
- TFD
- YKI
- ZKJ
- ZLJ
- ZMJ
Show the answer
ZLJ — C to F is +3, A to D is +3 and T to W is +3. So W + 3 = Z, I + 3 = L and G + 3 = J. The code is ZLJ.
Question 2 · Letter Analogies
Which pair completes the analogy? “CM” is to “FP” as “WR” is to ___
- AV
- IS
- TO
- YU
- ZU
Show the answer
ZU — C to F is +3, and M to P is +3. W + 3 = Z and R + 3 = U, so the answer is ZU.
Question 3 · Number-Word Codes
What is the code for ROOT? In a code, “THORN” is written “91472”.
- 4749
- 7429
- 7449
- 9447
- 9449
Show the answer
7449 — From THORN = 91472: T = 9, H = 1, O = 4, R = 7, N = 2. So ROOT is 7449.
More verbal reasoning games
Island Hopper
Island voyage: five channels, changing weather and the Storm Channel
- Synonyms and Antonyms
- Word Pairs
- Complete a Word Pair
- Odd Ones Out
- Word Connections
5 channels · about 4–5 min
Archery Arena
Archery tournament: four ends, wind challenges and a podium
- Letter Equations
- Equation Balancing
- Complete the Sum
- Number Sequences
- Related Numbers
4 ends · about 5 min
Liked Codebreaker HQ? Unlock the whole Arcade
Every game, every level and the daily challenge are included in every Prep4All plan, with lessons, practice tests and mock exams. Every plan starts with a 7-day free trial.