1. If we go to a wedding and there are more than 367 people, there must be people from the same Amanome (not in the same year). Put m things into n empty drawers at will (m >；; N), then there must be at least two things in a drawer. Since there are 366 days in a year at most, at least two of these 367 people were born on the same day in the same month. This is equivalent to putting 367 things into 366 drawers, and at least two things are in the same drawer.

In winter, cats always hold their bodies in a ball shape when they sleep, because their bodies emit the least heat. In mathematics, an object with a certain volume and the smallest surface area is a sphere. Shrinking the cat into a sphere can reduce the contact area with the outside world, reduce the speed of heat exchange, reduce the speed of heat loss, save energy and keep the body temperature.

3. "Muller leye county illusion", also known as Arrow illusion. If you add two diagonal lines at both ends of a line segment and two diagonal lines at both ends of another line segment, the former is much longer than the latter. There is a theory about this illusion, which is called nerve inhibition theory. It believes that when two contours are close to each other, adjacent nerve groups on the retina will inhibit each other, leading to contour displacement and illusion.

4. The wheel is round in shape. The center of the circle is called the center of the circle, and the distance from any point on the circle to the center of the circle is equal. Make the wheel round, and the axle is at the center of the circle. When the wheel rolls on the ground, the distance between the axle and the ground is always equal to the radius of the wheel. So people sitting in the car can be pulled away smoothly by the car. If the wheel is deformed and not round, and the distance from the wheel to the axle is not equal, the car will not be stable again.

5. The blades of the fan are all odd. This is because odd blade combinations can bring more performance advantages than even blade combinations.

If the number of blades is even, forming a symmetrical arrangement, it is not only difficult to adjust the balance of the fan itself, but also easy to make the fan generate more * * * vibration at high speed, which will lead to the failure of the blades to bear the fatigue caused by * * * vibration for a long time, and finally lead to the occurrence of blade fracture and other situations. Therefore, the design of axial flow fan is mostly asymmetric odd blade design.

The same design concept is also reflected in the design of daily electric fans or propeller helicopters. If the fan is a three-leaf structure, the blades are wider and the roots are stronger, and the density of each part needs to be uniform; If it is a five-leaf structure, the leaves are narrow and the thickness and strength are relatively low.

6. The winning probability of two-color ball is low. The two-color ball consists of 33 red balls and 16 blue balls, and each lottery is basically maintained at 6 red balls and 1 blue balls, so the winning rate of the first prize of the two-color ball is117720000. Which means there's a one in a million chance. Although the probability is very low, there are many people buying lottery tickets because of the large population base in China, so in theory, someone can win the first prize.

7. Four-leaf clover is called "lucky grass".

Clover, the scientific name of alfalfa, is a perennial herb with only three leaflets. The leaves are heart-shaped, and so are the darker parts of the leaves. Four-leaf clover is produced by clover gene mutation, accounting for only one in 100 thousand. In other words, out of 100,000 alfalfa plants, you may only find one clover, because the probability is too small. Therefore, "four-leaf clover" is an internationally recognized symbol of luck.

8. Well covers are basically round.

This takes advantage of the fact that the diameters in the same circle are all equal. Only the circular manhole cover can't find the diagonal, so no matter how to move the manhole cover, the manhole cover won't fall off, and the workers working below will have safety guarantee. If it is designed as a triangle or a square, although the cover is larger than the manhole, it may still fall down. In fact, besides safety, there is another advantage of making the manhole cover round, which is convenient for transportation.

9. The weather is unpredictable.

This involves a mathematical definition-"chaos", that is, "extremely unstable to the initial value". The common "butterfly effect" is a chaotic phenomenon. In general, global weather models basically follow some known reasonable processes. Through several different simulation methods, according to slightly different initial conditions, the weatherman can predict the future weather changes.

However, the weather is a combination of a series of complex factors. Small changes in initial conditions will make the forecast results very different. At this time, the weather has entered a chaotic area. The longer the forecast time, the more likely it is to reach the chaotic point, so the more difficult it is to grasp the accuracy of weather forecast.

10, golden section 0.6 18.

0.6 18, an extremely fascinating and mysterious number, also known as the golden section law, was discovered by Pythagoras, a famous mathematician in ancient Greece, more than 2,500 years ago.

Once, Pythagoras passed by the blacksmith's workshop and was fascinated by the tinkling of iron. In order to uncover the secrets hidden in this crisp and pleasant voice. Pythagoras measured the dimensions of hammer and anvil and found that there was a very harmonious proportional relationship between them. When he got home, he took out another thread and divided it into two sections. After repeated comparisons, he finally decided that the ratio of 1:0.6 18 was the most beautiful.