1. Fill in "+"and "-"between the following numbers to make the calculation result 100. 1 2 3 4 5 6 7 8 9= 100

2.ABCD+ACD+CD= 1989, find a, b, c and d.

3.□4□□-3□89=3839.

4.1abcde× 3 = abcde1,and find a, b, c, d and e.

Second, find the law.

6. Find a rule to fill in the blanks

( 1)75,3,74,3,73,3,( ),( );

(2) 1,4,5,4,9,4,( ),( );

(3)3,2,6,2, 12,2,( ),( );

(4)76,2,75,3,74,4,( ),( );

(5)2,3,4,5,8,7,( ),( 0);

(6)2, 1,4, 1,8, 1,( ),( )。

7. Fill in the appropriate number in ().

( 1) 1, 1,2,3,5,8,( ),( );

(2)0,2,2,4,6, 10,( ),( );

(3) 1,3,4,7, 1 1, 18,( ),( );

(4) 1, 1, 1,3,5,9,( ),( );

(5)0, 1,2,3,6, 1 1,( ),( );

8. Find a rule and fill in the appropriate number in ().

( 1)0, 1,3,8,2 1,55,( );

(2)2,6, 12,20,30,42,( );

(3) 1,2,4,7, 1 1, 16,( )。

9. The following sequence has certain rules. Find out its changing law and fill in the appropriate number in ().

( 1) 1,6,7, 12, 13, 18, 19,( );

(2) 1,3,6,8, 16, 18,( ),( );

(3) 1,4,3,8,5, 12,7,( )

(4) 1000,970,200, 180,40,30,( ),( )。

Third, permutation and combination.

1 1. Xiaohua, Kobanawa Pony, three good friends, should stand together in a row and take a photo. Three people are vying to stand in the front row and can't take pictures. Later, the photographer thought of an idea and said, "Do you want me to take a picture of each of you standing in different positions?" Now everyone agrees. So, how many photos should the photographer take for them?

12.2 (1) Class Xiaoping, Xiao Ning, Xiaogang and Xiaochao arranged a small board to prepare for the "Six, One" performance. During the performance, the formation changed constantly. (All standing in a row) Let's see, how many formation changes are there during the Allegro performance?

13. "69" is still "69" in reverse. We call these two numbers that are the same backwards a pair of numbers. You can choose three of the five numbers "0, 1, 6, 9, 8". How many pairs of the same numbers can you make?

14. The flag has five colors, and three sides are randomly taken out to form a line, representing various signals. Q: How many different signals can * * * represent?

15. How many three digits can be formed by using the number 0, 1, 2, 3, 4?

Fourth, simple reasoning.

16. There are three boxes in red, yellow and blue. Two boxes are empty. There is a table tennis in one box. On the lid of each box, there is a sentence: "Table tennis is not here". The red box reads; The yellow box says "table tennis is not here"; The blue box says "Ping-pong is in the red box"; However, only one sentence is true. Think about it: which box is the table tennis in?

17. A, B, C and D play table tennis. Every two people must play a game. As a result, A played D, and A, B and C won the same number of games. How many games did Ding Sheng play?

18.a, b, c, d and e participated in the table tennis singles competition. Every two people have to play a game, and only one game can be played. It is stipulated that the winner gets 2 points and the loser gets 0 points. Now we know that the result of the game is: A and B tied for first place, C tied for third place, and D and E tied for fourth place. How many points does C get?

19. In the second grade, a math contest was held. Marin, Wang Qiang and Li Wei won the top three. It is known that Marin is not the first, Li Wei is not the first or the second, () is the first, () is the second and () is the third.

20. Four children weigh themselves, and A is heavier than B; B is lighter than c; C is heavier than a; Ding is the heaviest. What is the weight of these four children from light to heavy?