Math: There are 400 bricks and square bricks. White bricks penetrate the fence first, then blue bricks penetrate the interior wall, and so on. How many blue bricks are there?

Because a * * * uses 400 bricks, each brick is 1 area unit, so the wall area is 400, and because it is square, the side length is 20 units.

According to the requirements of the topic, the edge length of the outermost white tile is 20, the edge length of the second green tile from the outside to the inside is 18(20-2= 18, and both ends are reduced by one unit), the edge length of the third white tile is 16, and the edge length of the fourth green tile is 14. . . . . .

Therefore, the side lengths of green tiles are 18, 14, 10, 6 and 2 respectively.

The corresponding number of bricks is:

Side length18:18+18+(18-2)+(18-2) = 68, minus 2 is because the bricks at both ends of the square are calculated repeatedly.

Side length 14: 14 * 4-4 = 52.

Side length 10: 10 * 4-4 = 36

Side length 6: 6 * 4-4 = 20

Side length 2: 2 * 4-4 = 4

The sum of the green tiles of the above layers is 68+52+36+20+4= 180.

Therefore, there are 180 green tiles.

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