How to do a 6th grade math competition problem 10

A makes 1 10 a day, B makes 1 15 a day, and it should be used cooperatively.

1 (1 10 + 1 15) = 6 days.

6 days, A work efficiency 1 10;B work efficiency 1 15;A and B cooperation work efficiency 1 10 + 1 15 = 1 6;

It takes 10 days for A, so his productivity is 1/10. It took B fifteen days, so his productivity was one-fifteenth.

6 (days).

A does the work 1 10 per day

B does 1 15 jobs a day

Two teams cooperate, do 1 10 + 1 15 = 1 6 every day, so it takes 6 days for two teams to cooperate.

1/10x+1/15x=1

The answer is your own.

Otherwise you won't understand.

Ahem cough inside... No way.

6 days Do the math yourself.

A's workload in a day is 1 10, and B's workload in a day is 1 15, and this work is regarded as a unit "one" 1 (1 10 + 1 15) = 6 (days).

If the workload is 1, A can do 1 10 per day, and B can do 1 15 per day, then the two teams can work together and do 1 10 + 1 15 = 1 6 per day, so it will take 6 days for the two teams to cooperate

From the title: Suppose this works as 1

Then A does 1 10 a day, B does 1 15 a day, and the two teams cooperate, that is, A does it in one day + B does it in one day = 1 10 + 1 15 = 1 6

The number of days is 1 (1 6) = 6 (days).

If you get all right, you can get 20*5=100 points.

For each mistake, it will be 5 + 2 = 7 points less than 100 points.

Li Ming scored 65 points, 100-65 = 35 points less than 100 points, so he did 35 7 = 5 wrong way.

So he got it right 20-5=15! Adopt!

First of all, we must understand how many points are less for doing a wrong question, not only do you not give points for a wrong question, but also deduct 2 again, so a total of 5 + 2 = 7 points are missing for a wrong question, assuming that he does all the right things, you can get 100 points, but only 65, so with 100-65 is the deduction of points 35, a wrong question is deducted 7 points, a total of 35 deductions, just use 35 7 = 5 questions, this is the number of wrong questions, the number of questions that are required to be right, use 20-5 = 15 questions.

Total score: 20 5 = 100 points.

Lost points: 100-65 = 35 points.

Incorrect: 35 (5+2)=5

True: 20-5=15

15 correct answers and 5 incorrect answers.

Hypothetical Method:

Assuming that they all get it right, they should get 20 5 = 100 points, 100-65 = 35 points more than the actual score, and the difference between the score of doing 1 question correctly and not doing 1 question wrong is 5 + 2 = 7 points; So, do 35 7 = 5 questions incorrectly and 20-5 = 15 questions correctly.

Equation solution: Set the correct x problem.

5x-（20-x）×2=65

solution, x=15

Solution: Let Li Ming do the right problem as x, and make or not do the problem as: 20-x;

5x+（20-x）*（2）=65

5x-40+2x=65

7x-40=65

7x=105x=15

Solution: If Li Ming did the x question correctly, then it is obvious that the question he did wrong and did not do is the 20-x question.

The column equation is as follows:

5x-2（20-x）=65

5x-40+2x=65

7x=105

x=15Answer: Li Ming got 15 questions right.

x+y=20

5x-2y=65

So do it right x=15

Wrong y=5

Suppose you do the right x lane, you do the wrong 20-x way.

5x-2x（20-x）=65

7x=105

x=15, so he got 15 questions right.

20x5=100

7x50=35

65 5=13 [Question].

Answer: Li Ming got a total of 13 questions right.

Because in the sixth grade of primary school, I only learned the one-dimensional one-dimensional equation, so I could only solve the above Olympiad numbers according to the one-dimensional one-dimensional equation.

So many of the above are also too stupid, and they should actually be solved like this:

Solution, assuming that you get the x question right, you get the wrong 20-x question.

So, there is: 5x-2*(20-x)=44

The solution is x=12

Answer: I got 12 questions right.

If all 12 are correct, then there should be 5 20 = 100 points;

He scored 44 points and lost 100-44=56 points;

If you start to reduce from the full score, you will lose 2 + 5 = 7 points if you make a mistake (not only will you not get the score but you will also be deducted), (if you don't do it, you will lose five points);

Because he did it all, it was either wrong or right, and there was only one case of losing 7 points.

That is, 56 7 = 8 wrong and 20-8 = 12 wrong.

Suppose you are clearly correct for a question x, not for y (because you have done every question, so it is not counted), and if you do a wrong question for z

A total of 20 questions!!

5x (the score of doing it right) - 2z (the score of doing it wrong) = 44x (the score of doing it right) + z (the score of the wrong question) = 20 (the total number of questions) The answer is as follows:

5x-2y=44

x+y=20

x=20-y

5(20-y)-2y=44

100-5y-2y=44

7y=-56

y=8x=y=20

y=8x=12

5 times 20 = 100 (points).

100-44 = 56 (points).

56 divided by (5+2)=8 (question).False 20-8=12 (question).Right.

Or set x questions correctly and y wrong questions.

5x-2y=44

x+y=20

x=20-y

5(20-y)-2y=44

100-5y-2y=44

7y=-56

y=8x=y=20

y=8x=12

Set x questions correctly and y wrong questions.

5x-2y=44

x+y=20

x=20-y

5(20-y)-2y=44

100-5y-2y=44

7y=-56

y=8x=y=20

y=8x=12

Solution: If Xiaoqiang does the x question correctly, then Xiaoqiang does the wrong (20-x) question.

According to the meaning of the topic, list the equations:

5x-2（20-x）=58

5x-40+2x =58

7x-40 =58

7x = 58+40

7x =98

x=14 is wrong: 20-14=6 (lane).

Answer: Xiaoqiang got 6 questions wrong.

The first full score is 20x5=100 points.

scored 58 points, 2 points were deducted for doing a wrong question, and he didn't even score a score for doing it right, and 2 points were deducted, which means that he lost 7 points for doing a wrong question.

100-58 = 42 points, he lost 42 points and divided 42 by 7 = 6, answer: "I got 6 questions wrong".

Solution: Set Xiaoqiang to do all the opposite.

20x5 = 100 points.

10-58 = 42 points.

42 (5-2) = 14 questions.

20-14=6 questions.

Answer: Xiaoqiang got 6 questions wrong.

/2=42/2

21 [Question] Answer: Xiaoqiang got 21 questions wrong.