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Mathematical Puzzles
This array of 9 nines contains 8 staight lines

 
Tue Mar 01, 2011 4:17 am  by tartle

This array of 9 nines contains 8 staight lines, each totalling 27 (3 accross, 3 down, 2 diagonal). Show how to move 4 nines to a new positions to make 10 straight lines, each totalling 27.
 
   
Tue Feb 11, 2014 10:42 am  by L

I tried to upload an image of my solution but I don't seem able to; so here is my best spoken explanation.

Move the corner nines (from a standard 3x3 array):
999

999

999

Move them away from the others so as to create a 3x5 matrix with 9's in cells:
a1,a3,a5
b2,b3,b4
c1,c3,c5

This creates 3 horizontal lines, one vertical line and six diagonal lines.[/img]
 
   
Tue Feb 11, 2014 10:49 am  by L

Edit:

It is actually neater to consider a 5x5 matrix with 9's in cells:

a1, a3, a5
c2, c3, c4
e1, e3, e5

This makes the lines clearer than in the 3x5 version.
 
   
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