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'Knight's Swap' printed from http://nrich.maths.org/
Several people decided that 16 moves were needed to swap the
stars and moons. The really interesting part is the ways they
invented to tell us what the moves were ...
Joshua (Brooklands
Primary School, Suffolk) numbered the squares 1 to 9 like this:
He says, "I could do the swap of the moons and stars in 16
moves:
 star at 7 goes to 6
 moon at 1 goes to 8
 star at 6 goes to 1
 moon at 3 goes to 4
 star at 9 goes to 2
 moon at 4 goes to 9
 moon at 8 goes to 3
 star at 2 goes to 7

 moon at 3 goes to 4
 moon at 9 goes to 2
 moon at 4 goes to 9
 star at 7 goes to 6
 moon at 2 goes to 7
 star at 1 goes to 8
 star at 6 goes to 1
 star at 8 goes to 3"

Thomas (Tattingstone
School, UK) used the gameboard like a map grid.
 Star 1 to B3
 Star 2 to A2
 Moon 1 to B1
 Moon 2 to C2
 Star 1 to C1
 Star 2 to C3
 Moon 1 to A3
 Moon 2 to A1

 Star 1 to A2
 Star 2 to B1
 Moon 1 to C2
 Moon 2 to B3
 Star 1 to C3
 Star 2 to A3
 Moon 1 to A1
 Moon 2 to C1

Jaimee
(Tattingstone School, UK) gave each square a letter and called the
Stars S1 and S2, and the Moons M1 and M2.
 M1 to F
 S1 to B
 M1 to G
 S2 to D
 M2 to H

 S2 to C
 M2 to A
 M2 to F
 S1 to I
 M1 to B

 M2 to G
 S1 to D
 M1 to I
 S2 to H
 S2 to A
 S1 to C
