2. Three workshops in a factory 180 people. The number of people in the second workshop is three times that in the first workshop, 1 person is more. The number of people in the third workshop is half of that in the first workshop, and 1 person is even less. How many people are in each of the three workshops?

3.5 9s are added, subtracted, multiplied and divided, which is equal to 2 1. (Parentheses can be used) 9999 = 2 1

4. Eight eights divided by addition, subtraction, multiplication and division is equal to 1999. . (Parentheses can be used)

8 8 8 8 8 8 8 8= 1999

5,1,2, 5,13, 34, 89, (), () 6. Arrange 2004 squares in a row, and three children, A, B and C, take turns to dye them in turn. From the first one, A dyes one square red, B dyes two squares yellow, C dyes three squares blue, A dyes four squares red, B dyes five squares yellow and C dyes six squares blue … until all the squares are dyed. How many squares are dyed blue?

7.95 students form a rectangle to do problems, and the number of rows and columns is greater than 1. * * * How many arrangements are there?

8. Write several consecutive natural numbers so that their sum is 1680.

9. Divide the average values of the eight books 40, 44, 45, 63, 75, 78, 99 and 105 into two groups, so that the products of the four numbers in the two groups are equal.

10, 60 students line up for sightseeing in groups, with the same number of students in each group, no less than 6 and no more than 15. How many ways are there? How to divide it?

1 1, there is a rectangle, its length, width and height are three consecutive probability numbers, and its volume is 3360 cubic centimeters. What is its surface area?

12. Divide the nine numbers 30, 33, 42, 52, 65, 66, 67, 78, 105 into three groups, and write these three groups of numbers.

13, the number a is 9 greater than the number b, and the product of the two numbers is 792. What are the numbers A and B respectively?

14. The product of four consecutive odd numbers is 19305. What are these four odd numbers?

15. There are four children, one of whom is just older than the other 1 year. The age product of four children is 3204. How old is the oldest of these four children?

16. There are three natural numbers, A, B and C. Given that A× B = 30, B× C = 35, C× A = 42, what is the product of a×b×c?

17, a bunch of watermelons, sold the total of 1/4 and 5 for the first time, and the remaining 1/2 and 4 were sold for the second time, leaving 4. How many watermelons are there in this pile?

18. There are 780 students in Grade 5 and 6 in Jinxi Primary School. Among the students who go to the Mathematics Olympic School, 8/ 17 are fifth-grade students and 9/23 are sixth-grade students. So how many students in grades five and six are not from the Austrian school?

19, the circumference of a circle is 1.26 meters, and two ants start from both ends of a diameter at the same time and crawl along the circle. These two ants crawl 0.04m and 0.05m per second, respectively, and turn and crawl once every 1, 3s, 5s (consecutive odd numbers). Then, when they met, they had climbed for two seconds.

20. If six digits 1992□□ can be divisible by 105, then this six digits is ().