287.—­AN ACROSTIC PUZZLE.

There are twenty-six letters in the alphabet, giving 325 different pairs.  Every one of these pairs may be reversed, making 650 ways.  But every initial letter may be repeated as the final, producing 26 other ways.  The total is therefore 676 different pairs.  In other words, the answer is the square of the number of letters in the alphabet.

288.—­CHEQUERED BOARD DIVISIONS.

There are 255 different ways of cutting the board into two pieces of exactly the same size and shape.  Every way must involve one of the five cuts shown in Diagrams A, B, C, D, and E. To avoid repetitions by reversal and reflection, we need only consider cuts that enter at the points a, b, and c.  But the exit must always be at a point in a straight line from the entry through the centre.  This is the most important condition to remember.  In case B you cannot enter at a, or you will get the cut provided for in E. Similarly in C or D, you must not enter the key-line in the same direction as itself, or you will get A or B. If you are working on A or C and entering at a, you must consider joins at one end only of the key-line, or you will get repetitions.  In other cases you must consider joins at both ends of the key; but after leaving a in case D, turn always either to right or left—­use one direction only.  Figs. 1 and 2 are examples under A; 3 and 4 are examples under B; 5 and 6 come under C;

[Illustration]

and 7 is a pretty example of D. Of course, E is a peculiar type, and obviously admits of only one way of cutting, for you clearly cannot enter at b or c.

Here is a table of the results:—­

         a b c Ways. 
    A = 8 + 17 + 21 = 46
    B = 0 + 17 + 21 = 38
    C = 15 + 31 + 39 = 85
    D = 17 + 29 + 39 = 85
    E = 1 + 0 + 0 = 1
        —­ —­ —­ —–­
        41 94 120 255

I have not attempted the task of enumerating the ways of dividing a board 8 x 8—­that is, an ordinary chessboard.  Whatever the method adopted, the solution would entail considerable labour.

289.—­LIONS AND CROWNS.

[Illustration]

Here is the solution.  It will be seen that each of the four pieces (after making the cuts along the thick lines) is of exactly the same size and shape, and that each piece contains a lion and a crown.  Two of the pieces are shaded so as to make the solution quite clear to the eye.

290.—­BOARDS WITH AN ODD NUMBER OF SQUARES.

There are fifteen different ways of cutting the 5 x 5 board (with the central square removed) into two pieces of the same size and shape.  Limitations of space will not allow me to give diagrams of all these, but I will enable the reader to draw them all out for himself without the slightest difficulty.  At whatever point on the edge your cut enters, it must always end at a point on the edge, exactly opposite in a line through the centre of the square.  Thus, if you enter at point 1 (see Fig. 1) at the top, you must leave at point 1 at the bottom.  Now, 1 and 2 are the only two really different points of entry; if we use any others they will simply produce similar solutions.  The directions of the cuts in the following fifteen