Primary 2 math problems together, to teach the idea of problem solving. O O thank you

This is a chicken-rabbit cage problem.

How do I think there's something wrong with your algorithm. The right way to think is:

If you get all 12 questions right, you can get: 12*10=120 points.

10 points will be added for each correct question, and 5 points will be deducted for a wrong question, indicating that each wrong question is less: 10+5=15 points.

Xiao Ming has a total of less: 120-75 = 45 points, so Xiao Ming is wrong: 45 15 = 3 points.

This is a chicken-rabbit cage problem.

There's something wrong with your algorithm, and the right way to think is:

If all 12 questions are done correctly, you can get: 12 * 10 = 120 points, add 10 points for each correct question, and deduct 5 points for a wrong question, indicating that each wrong question is less: 10 + 5 = 15 points.

Xiao Ming has a total of less: 120-75 = 45 points, so Xiao Ming is wrong: 45 15 = 3 points.

Each question is worth 10 points, and 5 points are deducted for a wrong question, and he still gets 5 points.

12*10=120 is the total score of 12 questions.

120-75 = 45, total score - the score obtained, the result 45 is the deducted score.

45 5 = 9 questions, a total of 45 points were deducted, 5 points were deducted for each question, and the result was 9 questions wrong.

12-9 = 3 channels, i.e., 3 channels are done correctly.

This question is super easy to be fooled, and if you make a mistake, you will actually deduct 15 points, and I have been fooled before, so you should know.

Suppose you do 6 correct 60-30=30 Suppose 10 100-10=90 The result must be 9 Hahaha Forget it Sure enough, you take 1 and a half first, and compared with this number, there are fewer mistakes.

The process is not like this, the wrong question is less than 15 points, a total of 45 points less, 45 divided by 15 = 3, so three wrong questions

If all pairs: 12*10=120 points.

Actual score: 120-75 = 45 points.

Error: 45 (10+5) = 3 questions.

If you do a wrong question, you will not be given extra points, and five points will be deducted, which is 15 points, so, 45 15 = 3 questions.

Because 5 points will be deducted for an incorrect answer, it is equivalent to missing (10+5) points.

It should be: 10+5=15 45 15=5 The third step is wrong.

You've laid out the formula, and the lower part is fine. Three wrong, nine correct.

Very simple.

The idea of the third step is wrong.

Mistakes are equivalent to deducting 15 points, and 3 mistakes are made.

Isn't it wrong in this question, and if it loses 10 points, it will deduct 5 points??

It can be answered with the question of chickens and rabbits in the same cage; (12 10 75) (10 5) 3 in the end

1 There are 91 mangoes, peaches, and papayas, and it is known that the number of peaches is 5 times that of mangoes, and the number of papayas is 7 times that of mangoes. How many mangoes, peaches, and papayas are there?

Mango: 1x7=7 (pcs).

Peaches: 5x7=35 (pcs).

Papaya: 7x7=49 (pcs).

2 This year, the big turtle is twice as old as the young turtle; 20 years ago, the big turtle was 3 times the age of the young turtle; Thirty years ago, the big turtle was 5 times the age of the young turtle. Q: How old are the big turtles and the baby turtles?

20 (5-3) = 10 (years).

Baby turtle: 10x4 = 40 (years).

large tortoise; 40x2=80 (years).

3 The kindergarten aunt gave chocolates to the children, each of them 4 pieces, and the remaining 3 pieces, each person was given 5 pieces, and there was a shortage of 4 pieces. Please do the math, how many children are there? How many chocolates are there?

Number of people: (3+4) (5-4)=7 (people).

Number of chocolates: 4x7+3=31 (pieces).

4 And there was a bell, and it struck six times at six o'clock. If it takes 10 seconds to knock 6 times, think about it, how many seconds does it take to knock 10 times?

Knock 6 times, there are 5 intervals, each interval: 10 5 = 2 (seconds).

Knock 10 times, 9 intervals: used: 9x2=18 (seconds).

5 A bicycle has 2 wheels, a tricycle has 3 wheels, there are 9 bicycles and tricycles in the carport, Xiaowen counted, there are 24 wheels, do you know how many bicycles there are, how many tricycles there are?

Suppose each car removes 2 wheels, then 2x9=18 wheels are removed, and 24-18=6 (pcs) is left for the tricycle, each tricycle has 1 wheel left, 6 wheels have 6 tricycles, and bicycles have: 9-6=3 (units).

6 How long does it take for a snail to climb a 25 cm long bamboo pole, 3 minutes for every 5 cm climbed, and 1 minute for rest, how long does it take for it to climb from the bottom of the bamboo pole to the top?

3x5 = 15 (min).

1x4=4 (min).

15 + 4 = 19 (points).

(Is this a 2nd grade question?) ）

2nd grade? Probably not

Solution: Set Li planted x trees, Liu planted Y trees, and Fang planted Z trees.

From the title, it can be seen that x+y=18,x+z=23,y+z=21 Therefore: 2x+2y+2z=18+23+21=62, that is, x+y+z=31 so:

Fang: x+y+z-(x+y)=31-18=13 (tree) Li: 23-13=10 (tree).

Liu: 18-10=8 (trees).

Let Li be x, Liu be y, and square be z.

As can be seen from the title, x+y=18

x+z=23

y+z=21, x=18-y, substitute x+z=23

18-y+z=23①

y+z=21②

②：18+2z=44,z=13

Substituting z=13 into x+z=23 gives x=10

Substituting x=10 into x+y=18 gives y=8

x=10,y=8,z=13

Obviously, it means to arrange a sequence according to the time of play, and the big picture it gives can be judged that the boat is from left to right, so you should see the bird first, then the whole picture of the tower, and then you can only see half of it after passing the tower (and it is the right half), and finally the pavilion, which should be the logic and meaning (this is the question of the second grade now!). I have to say that it's very good, my God, but it's also drunk to turn the camera as a non-haired person).

First: The boat on ** is not Mr. Zhang's boat;

Second, according to the course of other ships, the course of Mr. Zhang's ship can be considered to be the same as his;

Third, the chronological order of the ship from far to near means the process of the ship gradually opening its destination from afar.

Combining the above three points, the answer is 2 1 4 3

The boat is on the left, traveling from left to right, and the first to meet is near, and the last to meet is far, so it is 2143

The correct answer is ).

Analysis: Because from far to near, you must see the birds in the sky first, and the specific attractions are not clear; And the pagoda is tall, the pavilion is short, of course, the pagoda is seen first, and the pavilion is seen last.

The boat goes from left to right, from far to near, when the boat walks, the first thing people see on the boat is the first, and the boat goes to the far right to see the last scene.

In the order of the ship from far to near, that is, the process of gradually approaching the nearby landscape buildings, the boat first sails to the seagull, then the pagoda, and finally the pavilion.

3, 1, 2, 4 This is in order from far to near.

The answer should be right, from far to near.

Personally, I don't think the original answer is wrong, so ask the teacher.

The first two parentheses are filled in "come soon", and the last ones are filled in "count". Count the duck nursery rhymes, come and count 24678

A catches three times as many fish as B, C catches twice as many fish as B, and C catches only one less fish than A, so it can be seen that A catches more fish than C is the number of fish caught by B, so B catches 1, A catches 3, and C catches 2.

Solution: 1 (3-2)=1 (piece).

1*(1+2+3) 3=2 (pieces).

C caught 2, B 1, and 2

Upstairs, the second grade hasn't learned equations yet! So, just do it with the equation!

Solution: 1 (3-2)=1 (piece).

1*(1+2+3) 3=2 (pieces).

C caught 2, B 1, and 2

Let B be Article A.

then A is 3a and C is 2a.

and 3a-2a=1

then a=1, then A fishes 3, B fishes 1, and C fishes 2.

x A = 3 * x B.

x C = 2 * x B.

x C = x A—1

The number stands for multiplication.

Number of fish caught by A = number of fish caught by B multiplied by 3

Number of fish caught by C = number of fish caught by B multiplied by 2

Number of fish caught by A - Number of fish caught by C = 1 = number of fish caught by B multiplied by 3 - Number of fish caught by B multiplied by 2 = number of fish caught by B.

Number of fish caught by A = number of fish caught by B Multiplied by 3 = 3

Number of fish caught by C = number of fish caught by B Multiplied by 2=2

So the number of fish caught by A, B and C are:

Condition 1: If Xiao Ming's book gives.

Little Red. 3 copies, just as much. It shows that Xiao Ming has 6 more books than Xiao Xiao Hong. Chain Royal.

Condition 2: Xiao Ming bought 3 times as many books as Xiao Hong, and regarded Xiao Hong's call as 1 time, and Xiao Ming had 2 times more books than Xiao Hong.

Getting condition 3: 6 books is twice as much. So 1 times is 3 books.

So: Xiao Hong has 3 books, Xiao Ming has 9 books.