1. There are three tigers, three cows and a boat on the east bank of the river. They are going to cross the river. If the boat can only carry two (two tigers, two cows, one tiger and one cow) at the same time, only one tiger and one cow can skate. Where there are more tigers than cows, tigers eat cows. Please design a plan to let these animals cross the west bank of the river safely. (Note: Only a skating tiger or cow can be brought as a boatman. Except for those who can skate, only another tiger or cow can be brought. )

2. Try to cut the existing pieces of paper into two squares and splice them into a big square with a proper method. (No more paper)

In the ten hours from midnight yesterday to ten o'clock this morning, how many times did the hour hand and the minute hand make right angles?

4. There is a 6X6 grid (that is, a grid has six rows and six columns). Try to fill the natural numbers from 1 to 36 into the grid respectively, so that the sum of every six numbers on each horizontal, vertical and diagonal line (that is, diagonal line) is equal.

5. In ⊿ ABC, AB=BC, and ∠ ABC = 100, point E is on AB, point D is on AC, and CE shares ∠ ACB, ∠ CBD = 20.

Try to find the degree of ∠CED.

6. In ⊿ ABC, AB = AC, ∠ A = 20. D is the point above AB, and E is the point above AC. Try to find the degree of ∠DEB.

7. Given a circle O (centered on point O), try to divide the circle into four equal parts with a compass.

8. There is a circle without a center. Try to find the center of this circle with only compasses. (Note: Only with compasses)

9. It is known that the lengths of three sides of a right-angled triangle are natural numbers, and the right-angled side is 12. Try to find the circumference of this triangle.

10. As shown, there are two squares. Please guide each square into two pieces, and two squares into four pieces, so that the shapes and sizes of these four pieces are the same, and each piece has the letters A, B, C and D..