Many J.

asked • 08/15/20

Help! What is the greatest number of white squares you can place so that each covers part of the blue square without overlapping one another?

You have a large pile of squares that each have a side length of 1 inch. One square is blue, while all the other squares are white. You want to arrange several white squares so they cover part of the blue square but don’t overlap with each other.


What is the greatest number of white squares you can place so that each covers part of the blue square without overlapping one another? (The entire blue square does not have to be covered, while the blue area that each white square covers must be nonzero.)

4 Answers By Expert Tutors

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Sava D. answered • 08/16/20

Tutor
4.9 (98)

Geometty expert

Many J.

Wouldn’t it be 5 squares? 1+2+2?
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08/16/20

Sava D.

tutor
No, 7. We need three bands of squares. The band in the middle can be adjusted so that the diagonal of the square is covered with three squares. The full length of one of the diagonals cannot be covered with one square. We can use two squares with side parallel to the diagonal, or three squares with side parallel to the diagonal: one covering the central part, and the little part of the square corner of each side covered by different square. We are left over with little corners on each side of the band, created by the three squares. We can place two adjacent squares covering each of these corners. So we got seven.
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08/16/20

Many J.

Is there a way to express this mathematically?
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08/16/20

Sava D.

tutor
Answer: 7 white squares.
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08/16/20

Sava D.

tutor
I will try to post an image with the solution.
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08/16/20

Nikhil S.

I also concluded 7, but I still haven't been able to prove that eight is not possible. Do you have a proof of this or an idea for one?
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08/17/20

Sava D.

tutor
My idea for reasoning is as follows. The two longest line segments in a square are the diagonals. We can cover one of the diagonals with no more than 3 squares. The rest of the square are two small triangles on each side of the central white square. Each of these triangles can be covered by 1 or 2 squares only, because the longest side is less than 1/2 units. Hence, the total number of squares that can cover the blue square is no more than 7.
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08/17/20

Nikhil S. answered • 08/17/20

Tutor
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Sava D.

tutor
Check my last note in the discussion with you and Many. That is the proof.
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08/17/20

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