In a cylindrical bottle with a bottom radius of 10 cm, the water depth is 8 cm. To put a piece of iron in the bottle, which is 8 cm in length and 15 cm in width and 15 cm in height, how many cm does the water surface rise when the iron is placed vertically in the water?

3.14 × 102 × 8 ^ (3.14 × 102-8 × 8) - 8, = 2512 ^ 250-8, = 10.048-8, = 2.048 (CM), a: the water surface has risen by 2.048 cm

The length of a classroom is 8 meters and the width is 6 meters. Now, how many square bricks do you need to use to pave the floor?

8 meters = 80 decimeters, 6 meters = 60 decimeters, 80 × 60 ^ (2 × 2) = 4800 ^ - 4 = 1200 (pieces); answer: at least 1200 such square bricks are needed

What are the 56 nationalities

1. Mongolian
Mongolian is a nation with a long history and rich in legend, living a nomadic life of "moving by water and grass". Most of the grasslands in China have left the footprints of Mongolian herdsmen, so they are known as the "proud son of Grassland". It is a traditional festival of Mongolian with a long history to hold the "Nadam" meeting every July and August when the livestock are fat, This is a sports and entertainment meeting held to celebrate the harvest. There are thrilling horse racing and wrestling, admirable archery, competitive chess, and fascinating songs and dances at the "Nadam" meeting, showing the unique characteristics of the grassland people
2. Hui nationality
In the 13th century, a large number of Muslims moved to China from Central Asia and integrated with the local Han, Uygur, Mongolian, etc. in the long historical process, through intermarriage and other factors, they gradually formed the Hui nationality, Every year, September is the holy month of Ramadan. All Hui people who are 12 years old and over 9 years old in good health should fast. After liberation, the State Council made the Eid al Fitr a legal holiday for Hui people
3. Miao Nationality
Miao's music and dance have a long history, and the arts and crafts such as cross stitch, embroidery, brocade, batik, and jewelry making are well-known in the world. The ancestors of Miao can be traced back to Chiyou tribe, which was active in the Central Plains in the primitive society. In the past, Miao believed in animism, worshipped nature, and worshipped ancestors. There were many festivals, including traditional festivals and sacrificial festivals, There are many festivals of Miao nationality, but they are called differently in different regions
4. Dai nationality
Dai is a nation with a long history. As far back as the first century A.D., there are records about Dai in Chinese historical books. After 1949, according to the wishes of Dai people, it was named "Dai". Dai people call themselves "Dai Yi" and "Dai Ya". Dai people generally believe in Hinayana Buddhism, and many festivals are related to Buddhist activities, This festival is called "sangkan Bimai" in Dai language. At that time, there will be a big feast for monks, relatives and friends to celebrate each other by splashing water
5. Su (L ǐ) Su (s ù) nationality
The Susu people were called "Lisu" in the Tang Dynasty. They first lived in the Jinsha River Valley at the junction of Sichuan and Yunnan. Later, they moved to Nujiang area in western Yunnan because of war and other reasons. On June 11, 1985, they established the Weixi Susu Autonomous County in Yunnan, It's equivalent to the Spring Festival, Torch Festival, harvest festival, Mid Autumn Festival, bath party, knife pole festival of the Han nationality. The "knife pole Festival" held on the eighth day of the second lunar month every year is exciting. It is said that the knife pole festival was set up to make the people of Su have the spirit of "dare to go up the sword mountain, dare to break through the fire sea"
6. Tibetan
Tibet is called "Bo" in Tibetan, and the Tibetans who live here call themselves "Boba". Known as the "roof of the world", Tibet is beautiful and magical, and is the main settlement of Tibetans. Among the 1.3 million people, Tibetans account for 95%, and are one of the ancient ethnic groups in China. Tibetans generally believe in Tibetan Buddhism, In the past, many traditional festivals were related to religious activities. Tibetan folk festivals include Tibetan new year, butter Lantern Festival, Buddha Bathing Festival and so on. The biggest traditional festival among Tibetan people is the Tibetan new year on the first day of the first month of the Tibetan calendar
7. Zhuang Nationality
Zhuang is the most populous ethnic minority in China. It is an indigenous ethnic group in the south of the five ridges. There are more than 20 self proclaimed ethnic groups, such as "Buzhuang", "butu", "BuNong" and "buyayi". After the founding of new China, it was collectively referred to as "Tong" and later changed to "Zhuang". Zhuang brocade, together with Yunjin in Nanjing, Shujin in Chengdu and song brocade in Suzhou, is known as "China's four famous brocade", Some people believe in Catholicism and Christianity. Famous festivals include the annual "March 3" Song Festival. The most grand festival is the Spring Festival, followed by the ghost festival on July 15, Tomb Sweeping Day, Mid Autumn Festival on August 15, as well as the Dragon Boat Festival, Double Ninth Festival, tasting new food, winter solstice, cattle spirits, and delivering stoves
8. Korean nationality
The Korean people are mainly distributed in Jilin, Heilongjiang and Liaoning provinces. Yanbian Korean Autonomous Prefecture is the main settlement area. The ancestors of the Korean people are the Korean people who moved from the Korean Peninsula to Northeast China, The five major festivals are: Yuanri (Spring Festival), Shangyuan (Lantern Festival), Hanshi (Qingming Festival), Dragon Boat Festival and Qiuxi. The Korean people have a long tradition of respecting the elderly. As early as the Lee Dynasty (1392-1910), September 9 was designated as the comfort day for the elderly
9. Gaoshan Nationality
Gaoshan ethnic group is the general name of the ethnic minorities in Taiwan Province, including more than ten ethnic groups. The name "Gaoshan ethnic group" is the general name of the ethnic groups in Taiwan Province after the victory of the Anti Japanese war in 1945, It is known as "forest treasure house". There are many festivals of Gaoshan Nationality. Most of their traditional festivals have strong religious color. "Harvest Festival" is also known as "Harvest Festival", "Harvest Festival" and "Harvest Festival", which is equivalent to the Spring Festival of Han nationality. It is the most grand festival of Gaoshan Nationality
10. Naxi
The ancient Qiang people of Naxi, who were originally nomadic in the Yellow River and Huangshui valley of Qinghai Province, moved southward to southwest Sichuan and Northwest Yunnan, and differentiated into different nationalities, including Naxi. Naxi means big or noble, while Xi means human. The Mosuo people of Naxi in Lijiang believe in gods and worship nature, It is believed that all things in the world are dominated by gods. The "Zhuanshan Festival" on July 25 of the lunar calendar is a public ceremony for people to worship natural entities
11. Bulang Nationality
Bulang people are the descendants of ancient Pu people. They were called "puziman" in Tang Dynasty and "Puman" in yuan, Ming and Qing Dynasty. Due to different living areas, Bulang people used to call themselves different. After the founding of new China, they were collectively called Bulang people according to their own national wishes. Bulang people used to worship polytheism and generally believed in Hinayana Buddhism, Many traditional festivals are mostly related to religious activities. Among them, the most distinctive festivals are: New Year's day, festival to village god, washing cattle's feet, etc.12
Most of the Achang people live in Yunnan. They are one of the earliest living people in Yunnan. Due to their different places of residence, they also call themselves "mengsa", "mengsa Chan", "duisar" and "Hansa". After liberation, they are collectively called Achang people. Huijie is a traditional gathering of Achang people, which is usually held in the middle of September every year. Achang people believe in Hinayana Buddhism, Huijie was originally a religious assembly. The main religious festivals include entering wa (closing the door), leaving wa (opening the door), burning white firewood, water splashing Festival, etc.13. Nu nationality
Nu nationality is one of the ancient ethnic groups in Yunnan, mainly distributed in Yunnan Province. Nu people call themselves "Nu Su", "a Nu" and "a long". They live together with Susu, Dulong, Tibetan, Bai, Han, Naxi and other ethnic groups. The traditional festivals of Nu nationality include New Year Festival, flower festival, grain God Festival, Mountain Forest Festival, among which the festival atmosphere is the strongest, Fairy Festival is a traditional folk festival of Nu people in Gongshan area of Yunnan Province
Ewenki people are mainly distributed in Heilongjiang Province in Northeast China and Inner Mongolia Autonomous Region. Ewenki people call themselves "people who live in big mountain forests". In the primeval forests of Daxinganling at 52 degrees north latitude, there are still footprints and cooking smoke of Ewenki people, The settlement is the hunting village of Aoluguya Ewenki, known as "Arctic village". Oboo Festival is a religious festival of Ewenki people, but it also holds some cultural and sports activities, so it has a wide range of mass
15. Oroqen nationality
"Oroqen" is a national name, which has two meanings, one is "people living on mountains", the other is "people using reindeer". Before the Qing Dynasty, Oroqen people were generally called "suolunbu", "dajibu" or "shilubu". After the founding of new China, Oroqen people were collectively referred to. Every year, June 18 is the traditional festival of Oroqen people - bonfire Festival, Oroqen people all light bonfires, sing and dance, and celebrate their own national festivals. There is also the custom of sending the God of fire to heaven on December 23
16. Hezhe Nationality
The ancestors of Hezhe people have been living and reproducing in Heilongjiang, Songhua and Wusuli rivers since ancient times. There were different names in history, such as "Heijin", "heizhen", "Hezhen", "Qileng" and "Hezhe". After the founding of new China, the unified name of Hezhe was Hezhe, which means people living in "Dongfang" and "downstream" of the river, Hezhen people, who have lived by fishing for generations, put lanterns on July 15 of the lunar calendar every year to pray for peace and harvest
17. Menba
According to Tibetan historical records, the ancestors of the Menba people have long lived in the Himalayan Mountains in southern Tibet. The Menba people mainly live in Motuo, Linzhi, Cuona and other counties in Tibet. "Menba" means people living in menyu. The Menba people follow the Tibetan calendar and have the same festivals as the Tibetans
18. Bai nationality
Bai people mainly live in Dali Bai Autonomous Prefecture of Yunnan Province, and the rest are distributed in all parts of Yunnan Province, Bijie Prefecture of Guizhou Province and Liangshan Prefecture of Sichuan Province. Bai people call themselves "Baihuo", "Baini", "Baizi" and so on, which means "white" in Chinese. In 1956, they were formally named Bai people according to the wishes of their own people, "March street", which has a history of more than one thousand years, is the most grand festival of Bai nationality. It is now named "march street national festival". In addition, there are "Torch Festival" (also known as Xinghui Festival) and other national festivals
19. Bao'an clan
Bao'an nationality is also known as "Bao'an Hui" because of its belief in Islam and similar customs with the local Hui nationality. In 1950, it was named Bao'an nationality according to the wishes of its people. Bao'an nationality is mainly distributed in Gansu Province, Northwest China. Bao'an nationality is commonly used in Chinese and mostly believes in Islam. The famous Bao'an waist knife has been produced for more than 100 years, especially loved by Tibetan people
20. Buyi Nationality
Buyi is a large ethnic minority in Southwest China. Before liberation, Buyi people were known as "Zhongjia", "Shuihu", "Yizu", "Tubian", "local" and "Raojia". In 1953, after negotiation, Buyi representatives from all over Guizhou Province formally used "Buyi" as the name of their own nation. Buyi people worship their ancestors, mainly believing in polytheism and nature worship, In addition to the Spring Festival, Dragon Boat Festival and Mid Autumn Festival, there are also "February 2", "March 3", "April 8" and "king of cattle Festival". The most grand festival is "June 6" of the lunar calendar
21. Daur nationality
Daur people mainly live in Inner Mongolia Autonomous Region and Heilongjiang Province, and a few live in Tacheng County, Xinjiang. "Daur" means "pioneer". The ethnic origin is Khitan. In the middle of the 17th century, in order to maintain the reunification of the motherland, this ethnic group launched the first armed fight against the invasion of tsarist Russia

In a cylindrical bottle with a bottom radius of 10 cm, the water depth is 8 cm. To put a piece of iron in the bottle, which is 8 cm in length and 15 cm in width and 15 cm in height, how many cm does the water surface rise when the iron is placed vertically in the water?