# Arrange 20 counters and remove 6 form them and not a single square can be indicated?

Arrange 20 counters in the form of a PLUS(+), as you can see in the image.

Now, how many different ways are there in which four counters will form a perfect square if considered alone? Thus the four counters composing each arm of the PLUS(+), and also there is four in the center of it, form squares.

Squares are also formed by the four counters marked A, the four marked B, and so on.

How will you remove 6 counters from it so that not a single square can be so indicated from those that are still there?

I think there are

21 squares

Counting

9 of this variety (2 on each leg plus the central one)

4 of this variety (can move this shape right, down or right+down).
These 4

And these four

I would remove these counters

• Checked you might ignored the square of length $2\sqrt{2}$ :D – Conifers Sep 17 at 11:04
• @Conifers Yes, you are right, thanks. – hexomino Sep 17 at 11:09