The numbers of line segments, angles, triangles, squares and rectangles are introduced. When counting, the key is to combine numbers with shapes, correctly classify them and find out the rules. For example: 1, there are () line segments below. 2. There are () corners in the picture below. 3. Count. There are () triangles in the picture below. A B C D 4, count * * * There are () rectangles under it. 5. Think about it: a * * * has () squares. 6. There are () triangles below. [Exercise] 1, there are () segments on the AF line. 2. There are () corners in the picture below. 3. There are () triangles in the picture below. O A B C D E F E A D B C 4, there are () triangles in the picture below. 5. There are () rectangles in the picture below. 6. There are () squares on the right. 7. 1 The weight of an elephant is equal to the weight of four cows, 1 The weight of a cow is equal to the weight of three ponies, and 1 The weight of a pony is just the same as that of four piglets. So 1 How many piglets does an elephant weigh? 8. bright primary school bought two tables and five chairs and handed them over to 1 10 yuan. The price of each table is three times that of each chair. How much is each table? 9. Xiao Qianghua 24 yuan bought three small notebooks and six large notebooks. It is known that three small notebooks and two large notebooks are equivalent in price. What are the prices of small notebooks and large notebooks respectively? 10, 2 cows and 4 sheep * * eat 27 kilograms of grass a day, 6 cows 15 sheep * * eat 90 kilograms of grass a day, 1 cow 1 sheep * * How many kilograms of grass a day? 1 1, Class A and B ***83, Class B and C ***86, Class C and D ***88. How many people are there in Class A and Class D? The second lecture odd-even natural numbers 1, 2, 3, 4 ... can be divided into two categories: one is a number divisible by 2, that is, 2, 4, 6, 8 ... are called even numbers; The other is a number that is not divisible by 2, that is, 1, 3, 5, 7 ... called odd number; 0 is a special number and can be regarded as an even number. Even number and odd number have the following laws: odd number = even number; Odd even number = odd number; Even number = even number; Odd number+odd number+...+odd number = odd number; Odd number+odd number+...+odd number = even number; Odd even even even+even+...+even = even; Odd × even = even; Even × even = even; Odd × odd = odd. Example11× 2+2× 3+3× 4+4× 5+...+15×16, is the result odd or even? The sum of three consecutive odd numbers is 15. What are their products? As shown in the picture, it is a plan view of a shallow lake. All curves in the diagram are lakeshore lines. A person crosses the lake, takes off his shoes when entering the water, and wears shoes when landing. If there is a point B, this person walks from point A (point A is in the water) to point B, and the sum of the number of times he takes off his shoes and the number of times he puts on his shoes is odd. So is point B on the shore or in the water? Explain why. [Exercise] Is it the sum of 1, 1+2× 3+4× 5+6× 7+ ... +49× 50 odd or even? 2. Take out the 1994 continuous natural number at will. Is their sum odd or even? 3, 1, 3, 5, 7 ... are called continuous odd numbers. If the sum of consecutive odd numbers of 1 1 happens to be 199 1, what is the smallest number among the numbers of 1 1? 4. Is the sum of1987+1989+1+1993+and ... +2 135 odd or even? 5. 1992 is the sum of 24 consecutive even numbers, of which what is the largest even number? 6. The average of four consecutive odd numbers is 8. What are four odd numbers? 7. The sum of three consecutive even numbers is greater than the smallest even number 14. What are three even numbers? 8, 3-9 is the sum of the products of the seven numbers multiplied by pairwise odd or even? 9. There are 26 buttons in 6 boxes. It is required that the number of buttons in each box must be odd. At the same time, no matter how many buttons you take, you can bring the whole box to you. How many buttons do you think are in the six boxes? 10, can you divide the 25 natural numbers of 1-25 into several groups so that the maximum number in each group is equal to the sum of other numbers in the group? 1 1, the first group has five questions, and the second group has four questions. If the total number of students is odd and the total number of questions is even, ask whether the number of students in the first group is odd or even.

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