G.C.H.Q. PUZZLES

The UK Government Communications Headquarters staff delight in producing really difficult puzzles (in their spare time). Here are five of their easier puzzles that still need brain power to solve. There is no shame in giving up but once you have looked at the answers remember you have lost the chance of solving them for yourself for ever. The GCHQ Puzzle Books are available from all good booksellers. These puzzles are taken from the first book.

1   Which is the odd one out ?  February 2nd., April 4th., June 6th., August 8th., October 10th. or December 12th.

2   I found a piece of paper the other day where someone had written out the alphabet in various ways and highlighted four words, GNU, EMU, FOX and a girl’s name. What was the girl’s name ?

3   What is the next number in this sequence:  2, 5, 8, 10, 13, 17, 18, 20 ?

4   In a hotel recently I saw a notice in the lobby made up of those white plastic letters that push into holes in the board and can be easily changed to give different messages. The notice said:

When I asked the proprietor how many rooms there were in the hotel, she smiled. “You’re the puzzle expert. The answer is here in the lobby.” So how many rooms were there ?

5   Which of these numbers is the odd one IN and why ? (In other words each number is odd one out, for some particular reason that you need to discover, except this one.)   4, 66, 121, 484, 1936.

Answers.

1   February 2nd.   All the other dates occur on the same day of the week in any given year. February 2nd. is always on a different day.

2   AMY.   The alphabet was written in columns 7, 8, 9 and 12 letters wide. The first was:

A B C D E F G
H  I  J K L M N
O P Q R S T U
V W X Y Z

You can see the word GNU. When you write out the alphabet in more columns. you will find the other words and the name, AMY.

3   25.   The sequence is just the numbers in increasing order which are made up of the sum of two squares, for example 5 = (2 x 2) + (1 x 1). This makes the next number in the series 25 which is (4 x 4) + (3 x 3).

4   Ten rooms.   The words are an anagram of numbers so, by taking off letters ONETWOTHREEFOUR etc. up to NINE, I was left with the letters T E and N. Needless to say I replaced the letters.

5   484.   For the others, 4 is odd one out because it doesn’t divide by 11; 66 is odd one out because it is not a square; 121 is odd one out because it’s the only odd number; 1936 is odd one out as it doesn’t read the same forward and back.