1. Mathematical thinking training in summer vacation of grade two primary school
1, Wukong and Bajie accidentally broke into a digital maze. Only by answering six questions correctly and opening six doors can they go out smoothly. They answered five questions correctly, and there was only one left. The topic is:1-2+3-4+5-6+...-96+97-98+99. Kid, can you help Wukong and Bajie get out of the maze smoothly? The answers are added and subtracted to form a long string. This kind of problem can be calculated in groups, and the grouping of this problem should be considered from a large number. The specific analysis is as follows:
1-2+3-4+5-6+……-96+97-98+99
=99-98+97-96+……+5-4+3-2+ 1
= (99-98)+(97-96)+...+(5-4)+(3+2)+1(98/2-48, a * * * can be divided into 48 groups).
= 1*48+ 1
=49
2. Chickens and rabbits are in the same cage. a * * * has a head of 16 and 52 legs. There are () rabbits and () chickens in the cage.
Answer: Hypothetical method:
Assuming that all chickens are: 2 16=32 (only) and those with few feet are: 52-32=20 (only), then rabbits are: 20(4-2)= 10 (only) and chickens are:16-.
3、2+4+6+8+ 10+ 12+ 14+ 16+ 18=()
Answer: If this question is calculated in the order from left to right, it is more troublesome and prone to mistakes. Looking at these numbers carefully, we find that 2 and18,4 and16,6 and14,8 and 12 can all add up to 20, so we can use the method of rounding up 20 to calculate more simply.
2+ 18+4+ 16+6+ 14+8+ 12+ 10
=20+20+20+20+ 10
=90
2. Mathematical thinking training in summer vacation for the second grade of primary school.
1. Find the pattern and fill in the numbers: 4,8, 12,16,20, (), ().
3、 1、6、2、 12、3、()、()
Second, the sum of a two-digit number, a number on a ten-digit number and a number on a one-digit number is 10. If the positions of these two digits are exchanged, the number obtained is 36 less than the original number, and this two-digit number is ().
There are ***80 books on two shelves. Take eight books from the first shelf and put them on the second shelf. The number of books on the two shelves is equal. It turns out that there are () books on the first shelf.
4. There are 10 red beads and 10 black beads in the pocket. Now take at least () beads out of your pocket and make sure that the two beads are the same color.
Five, a car from Nanjing to Shanghai, along the way stop at Zhenjiang, Changzhou, Wuxi, Suzhou four stations, the railway department to prepare () different tickets for this train.
Grandpa is 74 years old this year. 10 years ago, his age was eight times that of his grandson, and this year he is () years old.
Seven, 1 bottle of oil weighs 600 grams. After eating half of the oil, weigh the bottle together, leaving 450 grams, and there is () grams of oil in the bottle.
Eight, a cup of milk, Xiaomei first drank half a cup, filled the cup with cold boiled water, drank half a cup, and filled it with cold boiled water. Finally, Xiaomei drank it all and asked her to drink () a glass of milk.
Nine, 1 ~ 9 these nine numbers, take two numbers at a time, the sum of these two numbers must be greater than 10, there are () ways to take.
10. An insect, from larva to adult, grows 1 times every day, and 16 days can grow to 40mm, and it takes () days to grow to 20mm.
3. Mathematical thinking training in summer vacation for the second grade of primary school
There are three people, Xiao Ming, Xiao Mei and Xiao Liang, standing in a row. There are several ways to stop () Answer: 1. Xiaoming, Xiao Mei and Xiao Liang; 2. Xiaoming, Xiao Liang and Xiao Mei; 3. Xiao Mei, Xiaoming and Xiao Liang; 4. Xiao Mei, Xiao Liang and Xiaoming; 5. Xiaoliang.
There is a road near the home of Boiling Sheep, which is 63 meters long. In order to welcome the Spring Festival, colorful flags should be inserted from beginning to end. Insert one side every 7 meters. How many sides should I insert a colorful flag?
Answer: 637+ 1 = 10 (surface). You need+1 because you need to insert colorful flags at the head and tail.
The sum of a and b is 20, and the difference is 6. What are the numbers A and B?
Answer: A =(20+6)2= 13, B =(20-6)2=7.
4. Xiaohong asked her mother how old she was, and her mother said, Add my age to 10, then multiply it by 5, subtract 25, and divide it by 2, which is exactly 100 years old. How old is Xiaohong's mother?
Answer: The last step in solving the problem is to divide by 2 to get 100 years old, that is to say, before dividing by 2, it is 1002=200, and after subtracting 25, it is 200+25=225. Similarly, if you don't multiply by 5, it is 2255=45, and if you don't add 10, it is 35. So,
The small animals in the forest held a sports meeting. Pork chop 13, rabbit ranked fifth. How many small animals do pigs have to surpass to be tied for fifth place with rabbits?
Answer: There are seven small animals between the rabbit and the pig, so the pig only needs more than seven small animals.
4. Mathematical thinking training in summer vacation for the second grade of primary school.
1, a circle of trees was planted around the square playground, and trees were planted at all four corners, with every two trees separated by 5 meters. A and B start from a corner at the same time and go in different directions. A is twice as fast as B. After turning a corner, B meets A on the fifth tree (the tree in the corner is regarded as the first tree). How many trees are planted around the playground? Answer: Because A's speed is twice that of B, so B walked on one side of the playground, A walked on both sides, B turned a corner and came to the fifth tree. In fact, four intervals are used, so A should take eight intervals. The tree I met was the ninth tree A walked after turning a corner, so there were 9+4= 13 trees here. There are (13- 1)4=48 trees around the playground.
There are five children in the class. The teacher gave everyone an apple and the first child 1 apple. Give the second child three apples. Give the third child five apples. And so on, give the fifth child 9 apples. Q: Is the total number of apples * * * odd or even?
Answer: 1+3+5+7+9= 15 (pieces) The answer is odd. But in this problem, we found that every child gave an odd number of apples. And the total number is odd. As we know, odd numbers add up to odd numbers. So the final answer is strange.
3. A piece of chalk has two heads. How many heads does a piece of chalk have?
Answer: 2x4=8, three and a half pieces of chalk are equivalent to four pieces, and three and a half pieces of chalk have eight heads.
Plant trees on both sides of the 80-meter-long garden. Plant one tree and two plants every 10 meter. How many trees will be planted?
Answer: To plant trees on both sides of an 80-meter-long expressway, we should first consider how many trees to plant on one side, and plant 1 tree at both ends every1meter. There are 8 trees at 80 meters, which means there are 8 gaps in the middle, so we can plant 9 trees on one side and 9 trees on both sides, which is 9+9 = 65433.
5. Calculation: 56+ 18+4436+37+63
Answer: add three numbers. We can add two numbers that can add up to one hundred, and then add the third number to their sum. In this way, it is necessary to change the operation order of the formula. In order to change the order of operations, we usually use parentheses. For brackets, it is the first time for students to know each other. The teacher can explain the use of brackets here properly, so as to lay the foundation for later study. If students have some difficulties in understanding brackets, they can also use the methods of drawing lines and rounding in Example 1 and Example 2.
56+ 18+4436+37+63
=56+44+ 18=36+(37+63)
= 100+ 18=36+ 100
= 1 18= 136
5. Mathematical thinking training in summer vacation for the second grade of primary school.
1. One day, Big Head's son was making a puzzle: Find1+2+3+4+5+6+99+100+99++13+12+/kloc. If he can't do it, ask the little head dad, and neither can the little head dad. Can you help the big head son calculate it? The answer is to observe this question first. If you add 9+8+7+...+3+2+ 1 at the back, you can use the middle number * the middle number to calculate. The specific analysis is as follows:
1+2+3+4+5+6+……+99+ 100+99+……+ 13+ 12+ 1 1+ 10
= 12+3+4+5+6+……+99+ 100+99+……+ 13+ 12+ 1 1+9+8+7+6+5+4+3+2+ 1-(9+8+7+6+5+4+3+2+ 1)
= 100* 100-45
= 10000-45
=9955
2. A small snail climbed up from the bottom of the ditch, which was 20 cm deep. It takes 2 minutes for the snail to climb 4 cm, and then it stops 1 minute. How long does it take the snail to climb out of the ditch () minutes?
Answer: It takes 2+ 1=3 (minutes) to climb 4cm each time, and 204 = 5 (4cm) of 20cm takes 35= 15 (minutes), but the last time you climb out of the ditch, you don't need to stop 1 minute, so it's a * * *.
3. Li Nainai's family has 12 eggs, and she also keeps a hen with 1 egg every day. Li Nainai's family eats two eggs every day, and her eggs can last () days.
Answer: You can eat 1 original egg and 1 natural egg every day for 12 days.
4. The three children are 8 years old, 9 years old and 10 years old. Xiao Lei is older than Xiaohui, and Xiaoling is older than Xiaohui, but she is less than 9 years old. Xiao Lei is old, Xiaoling is old and Xiaohui is old.
Answer: Xiao Lei is 9 years old, Xiaoling 10 years old and Xiaohui is 8 years old.
The store bought 6 boxes of balls and sold 8 balls every day for 5 days. The waiter rearranged it, and the remaining balls were just packed in 2 boxes. How many balls are there in each box?
Answer: If you sell 8 pieces every day for 5 consecutive days, you will sell 58=40 pieces. 6 boxes of balls are newly added, and the rest are just filled with 2 boxes, so sell 6-2=4 (boxes); If you sell 40 and 4 boxes, each box has 404= 10 (pieces), then each box has 10 balls.