Question:
complete the magic square given below, so that the sum of the numbers in each row or in each column or along each diagonal is 15.
Solution:
Taking the diagonal that starts with 6:
$6+5+x=15 \Rightarrow x=4$
Now, taking the first row:
$6+1+x=15 \Rightarrow x=8$
Taking the last column:
$8+x+4=15 \Rightarrow x=3$
Taking the second column:
$1+5+x=15 \Rightarrow x=9$
Taking the second row:
$x+5+3=15 \Rightarrow x=7$
Taking the diagonal that begins with 8:
$8+5+x=15 \Rightarrow x=2$
