How do you write this math problem? 5. How to write this math problem?

Solution: Suppose you answered x questions correctly.

3x+(30-x)=78

3x+30-x=78

2x+30=78

2x=78-30

2x=48x=48/2

x=24 Answer: 24 questions are done correctly.

The above are all wrong, and the wrong answer is an extra point, not a subtraction! Wrong example: Answered x questions correctly.

3x-(30-x)=78

x=27 by: gokoquan - Level 5 2010-1-7 22:06

Suppose all 30 questions are answered incorrectly, Xiao Ming gets 30 points, and now he has a total of 78 points.

So the score for answering the question correctly: 78-30 = 48 (points).

Number of questions answered correctly: 48 (3-1) = 24 (questions).

Equation. Solution: Set him right on the X question.

3x+（30-x）=78

2x+30 =78

2x =48

x = 24.

Suppose all are correct.

A: He got 24 questions right.

It is 90 points for all right, 2 points less for one wrong question, 12 points less for now, 6 questions wrong and 24 questions answered correctly.

Suppose the full answer is correct: 30*3=90

Incorrect: (90-78) (3-1)=6

True: 30-6=24

3x30 = 90 points.

90-78 = 12 points.

Incorrect answer: 12 (3+1)=3 questions.

True: 30-3=27 channels.

Solution: If you do the correct x question, you will do the wrong (30-x) question.

3x+1(30-x)=78

3x+30-x =78

2x =48

x = 24 Answer: Get 24 questions right.

If he answers x correctly and y is wrong, then x+y=30, 3x-y=78, can solve x=27, y=3, so he answers 27 correctly.

Finally, what I wrote is a bit simple, bringing in the elimination method, that is, simplifying one of the unknowns and bringing in the other to achieve the solution of the equation.

purpose. At the end of solving the equation, you must remember to verify, firstly, it is necessary to solve the problem, and secondly, you can verify whether the answer you have solved is correct.

Multiply 12:3(y+1)=4(x+2)3y+3=4x+8

3y=4x + 8 － 3

3y = 4x + 5, then y = (4x + 5) 3 substitute y into the following equation: 3x 2[(4x + 5) 3] = 1 multiplication on both sides 3: 9x 2 (4x + 5) = 39x 8x 10 = 3

x=13 substitutes x back: y=(4 13 + 5) 3=19 The solution of the equation system is x=13, y=19

Solution 3(y+1)=4(x+2).

3y+3=4x+8

3y-4x=5

3y=5+4x

y=（5+4x）/3

Substitute y into the second equation.

3x-2（5+4x）/3=1

9x-10-8x=3

x=13y=（5+13×4）/3=19

6 and 5 6 solution analysis: using the method of opening the square, first open the square, and then carry out other operations, the same level of operations are calculated in order, and the different levels of operations are calculated first, and then the results can be obtained quickly.

The upper equation is , and the lower equation is

Method 1 (addition and subtraction):

2 + gives 4x-10y-4x+y=-6-3 simplified, -9y=-9

y=1, substituting or medium, we get x=1

Method 2 volt line (substitution method):

Obtained by shifting terms, y=4x-3

Substituting Yunnaqi into , 2x-5(4x-3) = simplified, -18x+15=-3

x=1, substitution in the lack of y=1

1) Substitution method:

y=4x-3 is obtained from the pre-starvation rotten cherry blossom Qing formula, and substituted by the formula, 2x-5(4x-3)=-3

x=1, substitute y=4x-3, and get y=1.

2) Addition and Subtraction:

Formula 2+ formula, 10y+y=-9, song shed.

y=1, and substituting the formula, 2x-5=-3, x=1.

2x - 5y = 3（1）

4x + y = 3（2）

Substitution method: pickpocketing.

2) Deformation can be obtained:

y = 3 + 4x（3）

3) Substitution (1) obtained.

2x - 5（﹣3 + 4x）= 3

Solution: x = 1, then y = 1

Addition and subtraction: type this caution 2) both sides of the equation multiply by 5 De Bu Jing:

20x + 5y = 15（3）

3) and (1) are added together:

18x = 18

x = 1, then y = 1

2x-5y=-3

4x+y=-3

Addition and subtraction calendar cautious: give both sides of the formula multiplied by 2.

4x-10y=-6

Get 4x-4x-10y+y=-9

The solution gives y=1, y=1 substitution

This gives -4x+1=-3

Solution x=1

Substitution method: deform the limb foci to be filial piety y=4x-3 substitution formula 2x-5(4 -3)=-3

Get =1 and substitute x=1 to get y=1

Question 13, the abscissa and ordinate of the point in the first quadrant are equal, jumping to the 2nd, 5th, 8th, 11th, etcNumbers such as 2, 5, 8, 11 are divided by 3 by 2, and 35 3 = 11....2, which is also a remainder of 2, is 35 times the point in the first quadrant.

The horizontal and ordinate values are quotient 11 plus 1=12, so the final coordinate is (12,12).

Junior high school questions, put in the advanced mathematics column?

The result of the first two numbers adding up is the third number. Other words.

Insert 55 and 89 in parentheses.

Two adjacent numbers, divide the large number by the decimal number, and the result is getting closer and closer, and this number is the so-called "** split".

For example, 13 divided by 8 equals.

21 divided by 13 equals.

34 divided by 21 equals.

55 divided by 34 equals.

89 divided by 55 equals.

Fill in the blanks: 55 89

The rule is that the first two numbers add up to the last. The ratio is close.

Subtracting the previous term gives us a new sequence of numbers 1 2 3 5 8 13

Observing the new sequence, we can see that the third term is equal to the sum of the first two terms, and the fourth term is equal to the sum of the first two terms, that is, the second term and the third term, so the number after 13 should be 8+13=21, so the number series is 21+34=55, and 21 is followed by 13+21=34, so the original number series is 55+34=89

From 13 onwards, the ratio of the two numbers is approximately equal to that of the two numbers.

I can find that all of them are taken into ** ratio.