Requesting elementary school mathematics mixed operation questions and answers

(1)

There is a pasture with 27 cows, and the grass will be eaten in 6 days; if there are 23 cows, the grass will be eaten in 9 days; if the cows are raised 21 heads, how many days will it take to finish all the grass on the pasture? Note that grass in pastures is constantly growing, not static.

Explanation: Consider the amount of grass a cow eats in one day as the unit "1"

New grass growing every day (23*9-27*6) ÷ (9- 6) = 15

The original amount of grass that has grown is 23*9-15*9=72

Now 21 cows eat grass---15 of them eat every day New grass grows, and the other 6 cows eat the original grass

72÷(21-15)=12 days to finish eating

(2)

There was a box of pears in the box. The first person took half and more of the total number of pears, the second person took half and more of the remaining pears, and the third person took the second half and more of the remaining pears. The fourth person took half and more of the remaining ones from the third time, and the fifth person took half and more of the remaining ones from the fourth time. At this time, the pears in the box were just finished, and no one had half a pear in their hands. How many pears were originally in the box?

Explanation:

There are 0.5*2=1 before the fifth person takes it.

There are (0.5+1)*2= before the fourth person takes it. 3,

Before the third person took it, there were (0.5+3)*2=7,

Before the second person took it, there were (0.5+7)*2=15 ,

Before the first person took it, there were (0.5+15)*2=31 pears,

It turned out that *** had 31 pears.

(3)

Zhang San and Li Si each took a wine bottle with wine in it. They wanted to divide the wine evenly. Li Si first put his wine bottle in Pour the wine into Zhang San's bottle, so that the wine in Zhang San's bottle has doubled. Then pour Zhang San's wine into Li's fourth bottle, making the wine in Li's fourth bottle triple. After pouring it twice, it was still not evenly distributed. There were 160 grams of wine in the third bottle of Zhang and 120 grams of wine in the fourth bottle of Li. May I ask Zhang San and Li how much wine were in each of the bottles?

Explanation: Li Si first poured the wine from his own bottle into Zhang San's bottle, so that the wine in Zhang San's bottle doubled, and then poured Zhang San's wine into Li Si's bottle, so that the wine in Zhang San's bottle doubled. The wine in Li's bottle tripled.

Before Zhang San poured it over to Li Si----Li Si had 120÷3=40 grams, Zhang San had 16120-40=240 grams

Li Si poured it over Before Zhang San----Zhang San had 240÷2=120 grams, and Li Si had 16120-120=160 grams.

(4)

A, B, and C are all reading the same story book. There are 100 stories in the book. Everyone starts with a certain story and reads forward in order. It is known that A has read 75 stories, B has read 60 stories, and C has read 52 stories. So what is the minimum number of stories that A, B, and C have read together?

Explanation: B and C*** have read at least 652-100=12 stories together. A must read these 12 stories no matter where he starts.

Answer: A, B, and C*** have read at least 12 stories together

(5)

A, B, and C Water 100 pots of flowers at the same time. It is known that A has watered 78 pots, B has watered 68 pots, and C has watered 58 pots. How many pots of flowers have been watered by all three people?

Explanation: A and B must have 78+68-100=46 pots that have been watered together, and C has 100-58=42 that have not been watered, so there are at least 46 pots that have been watered by all three people. -42=4 (pots)

Answer: There are at least 4 pots of flowers that have been watered by 3 people.

(6)

There are a number of cards, each card has a number written on it, which is a multiple of 3 or a multiple of 4. Among them, the card marked with a multiple of 3 accounts for 2 /3, cards marked with multiples of 4 account for 3/4, and there are 15 cards marked with multiples of 12. So, how many cards are there in a day?

Answer: The multiples of 12 are 2/3+3/4-1=5/12, 15/(5/12)=36 (pieces)

Answer: These cards There are 36 cards in a ***.

(7)

The statistics of the mid-term exam results of a certain class of mathematics and English are as follows: 12 people scored 100 points in English, 10 people scored 100 points in mathematics, and two subjects

There were 3 people who got 100 points in both subjects, and 26 people who didn’t get 100 points in both subjects. How many students are there in this class?

Answer: There are 45 students in this class.

(8)

There are 58 people in the kindergarten learning piano, 43 people learning painting, and 37 people learning both piano and painting. Ask about those who only learn piano and those who only learn painting. How many

people are there?

The number of people who only learn piano: 58-37 = 21 (people)

The number of people who only learn painting: 43-37 = 6 (people)

(9 )

Students in Class 3 of fifth grade participate in extracurricular interest groups, and each student participates in at least one activity. Among them, 25 people participated in the nature interest group, 35 people participated in the art interest group, 27 people participated in the Chinese interest group, 12 people participated in the Chinese and art interest groups, and 8 people participated in the nature and art interest groups. Naturally, 9 people also participated in Chinese interest groups, and 4 people participated in all three subject interest groups: Chinese, art, and science. Find the number of students in this class.

Answer: The number of students in this class is 62.

(10)

There are 100 books in the library, and those who borrow books need to sign the books. It is known that among the 100 books, there are 33, 44 and 55 books signed by A, B and C respectively. Among them, 29 books are signed by both A and B, and 25 books are signed by both A and C. There are 36 books signed by B and C. Ask how many books in this batch of books are at least not borrowed by anyone from A, B, or C?

Explanation: The number of books that three people have read together is: A + B + C - (A, B + A, C + B, C) + A, B, C = 33 + 44 + 55 - (29 +25+36) + A, B, and C = 42 + A, B, and C. When A, B, and C are the largest, the three of them have read the most books, because A and C have only read 25 books together, which is more than A, B, and B and C* **have read very few of them, so A, B, and C have both read at most 25 books together.

The three of them have read a maximum of 42+25=67 (books), and the number of books that none of them have read is at least 100-67=33 (books)

This At least 33 of the batch of books have not been borrowed by any of A, B, and C.

(11).

There are 50 people in the class, 32 people can ride bicycles, 21 people can roller skate, and 8 people can do both. Please do both. How many people don’t know how to do it?

50—(30 + 21—8) = 7 (people)

Answer: There are 7 people who can’t do both.

(12)

There are 42 students in a class, 30 students participate in the sports team, and 25 students participate in the art team, and each student participates in at least one team.

How many people are participating in both teams in this class?

30 + 25—42 = 13 (people)

Answer: There are 13 people participating in both teams in this class.