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Question.

Transcription:

In a given magic square, if the sum of number in each row
and each column and both of the main diagonals are equal,
then the value of x is:

1) 10
2) 12
3) 8
4) 15

Source:INTSO Grade 3

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  • 1
    $\begingroup$ Is this question from an ongoing competition? If not, credit the source. $\endgroup$ – Maria Deleva Feb 4 '17 at 17:46
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The answer is:

12.

Right So, here's an image

enter image description here

Here's a description of the working:

As sum of all rows,columns and main diagonals are equal.
$$13+y+d=15+y+5 \implies d=7$$
$$ b+15+d=x+y+b \implies x+y=22$$ (using d=7) $$ 13+5+x=15+5+y \implies x-y=2 $$
So, solving the two equations in x and y, we get x=12 and y=10

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