(a) The divisor is close to integer division.

For this kind of problem, divide the divisor by the whole hundred.

For example, 1902 ÷ 197 =

1456÷202=

Think: 197≈200

Think about it: 202≈200

200×9= 1800

200×7= 1400

Determine the tester 9

Determine the tester 7

Do: do:

Because: 129 < 197 because: 42 < 202.

So: the trial quotient is correct, so: the trial quotient is correct.

(2) Close to the dividing line of □50 graduation

To do this kind of questions, we must first strengthen the oral arithmetic training of students150,250,350 ... this is a necessary condition for rapid and accurate quotient measurement. Secondly, it should be used flexibly in calculation.

For example, 765 ÷ 247 =

567÷ 152=

Think about it: 247≈250

Thinking: 152≈ 150

250×3=750

150×3=450

Determine the tester 3

Determine the tester 3

Do: do:

Because: 24 < 247 because:11<152.

So: the trial quotient is correct, so: the trial quotient is correct.

(3) The divisor is between □50 and whole hundred.

Because the divisor from □ 16 to □64 has its own characteristics, if the above method is still used, the quotient obtained will sometimes be inaccurate. We can take the maximum and minimum value of the divisor (whole hundred), then find the quotient respectively, and then find the average value of the sum of the two quotients. This average is the quotient we require or very close to what we require.

For example, 78 1÷ 136

13 16÷26 1

It is considered that: because: 78 1÷ 100 quotient 7 because: 13 16÷200 quotient 6.

781200 quotients 3

1316÷300quotients 4

(7+3)÷2=5

(6+4)÷2=5

So: Trial Quotient 5

So: Trial Quotient 5

Note: This method is also applicable to (2) above.

(4) How to reduce the number of trial quotients is the purpose of skillful quotients.

Because we use the approximate method, the trial quotient may be larger or smaller. At this time, teachers should explain to students the reasons for the changes in quotient and analyze and summarize the changes.

( 1)

divisor

Rounding becomes smaller.

The quotient may be getting bigger.

(2)

divisor

Rounding is getting bigger and bigger.

The quotient may get bigger and bigger.

The purpose of the above analysis is to enable students to quickly classify multi-digit division and find corresponding methods. So as to achieve skillful quotient and improve accuracy and speed. Of course, students should be able to do business accurately and quickly in order to achieve the effect of proficiency in business. Besides mastering the correct methods, we should practice more. As the saying goes, "Practice makes perfect", so proper practice is a necessary condition to improve the accuracy and speed of calculation.

Interesting problems in mathematics

1. There are 48 students participating in three sports competitions, but the number of participants in each activity is different, and there is a number "6". How many people participated in each of the three sports competitions?

Longlong and Liangliang go to the park to play and want to buy tickets, but they don't have enough money. Longlong lacks 4 yuan by 80 points, and Liangliang lacks 1 point. Their money together is still not enough. How much is the park ticket?

How many minutes does it take for three people to eat three tomatoes and six people to eat six tomatoes at the same time?

4. There are 10 cards, face up, 6 cards at a time. How many times have you turned the cards? Can all the cards face up?

Xiao Zhang bought 24 bottles of soda, and every four empty bottles can be exchanged for 1 bottle of soda. How many bottles of soda can Xiao Zhang drink?

Age problem

1. The sum of four people's ages is 77 years old, and the youngest 10 years old. The sum of the ages of the oldest and youngest people is seven years older than that of the other two. How old is the oldest person?

On my father's 50th birthday, my brother said, "When I grow to my brother's present age, the sum of my brother and I will be equal to my father's then age." So how old is my brother this year?

The average age of Party A, Party B and Party C is 42 years old. If Party A's age is increased by 7 years, Party B's age is doubled, and Party C's age is reduced by half, which is equal. How old is Party A?

In a family, the total age of all members is 73 years old. There are father, mother, a daughter and a son at home. Father is 3 years older than mother, and daughter is 2 years older than son. Four years ago, the total age of all the people in the family was 58. How old is each member of the family now?

5. 10 years ago, Wu Hao was seven times older than his son. 15 later, Wu Hao is twice as old as his son. How old are the father and son now?

Cross-filling type

1. Fill the seven numbers 0~6 into ○, and each number appears exactly once. It is a two-digit integer expression.

○×○=○÷○=○

2. The following formula consists of 9 numbers of 1~9. The position of 5 is already known, and other figures will be added.

□*□=5□

□□÷□*□=□

3. Fill 1~9 into the following equation to make the equation hold (give some figures).

□7×□=6□=□3-□□

4. Fill in 9 numbers 1 ~ 9 in the blank of the following formula, one of which is known, and only one number can be filled in each blank to make the formula effective:

□□□÷□□=□-□=□-7

5. The nine numbers1~ 9 are filled in the blanks of the following formula respectively, and only one number is allowed in each blank to make the formula effective:

The chicken and the rabbit are in the same cage.

1. Xiaoli has 100 coins in her piggy bank. She changed all twenty cents into five cents, and the total number of coins became 73. Then she changed a penny into an equivalent nickel, and the total number of coins became 33. So there's something in her piggy bank.

Yuan.

2. Three kinds of insects *** 18, * * * have 20 pairs of wings 1 16 legs. Among them, each spider has 8 legs and no wings, each dragonfly has 2 pairs of wings and 6 legs, and cicada has 6 legs. How many are these three kinds of insects?

3. A math test paper has only 25 multiple-choice questions. Get 4 points for doing a right question, and deduct 1 point for doing a wrong question; If you don't do it, you won't score or deduct points. If Xiaoming got 78 points in the exam, then he did the right thing.

Problem, doing something wrong

Question, don't do it.

Title.

4. A magazine, 2 yuan 50 cents per issue, once a year 12. Some students in a class book for half a year, and some book for a whole year, and they want 1320 yuan. If you book the whole year for half a year and the whole year for half a year, then * * * needs to book 1245 yuan. How many students are there in this class?

It is known that students A, B and C * * have solved 100 math problems, and each of them has solved 60 of them. If the problem solved by only 1 person is called "difficult problem" and the problem solved by all three people is called "easy problem", how many ways are there for "difficult problem" than "easy problem"?

Third grade exercises

1. Calculation: 9998+998+99+9+6

2. Calculate174+177+183+182+176+180+179+.

3. There are 70 boys and several girls in a school taking part in the math contest, with an average score of 63, 60 for boys and 70 for girls. How many girls are there in the school?

4.7 The average number is 28. If these seven numbers are arranged in a row, the average of the first four numbers is 26, and the average of the last four numbers is 33. What's the fourth number?

5. 1,2,6,24, 120,(),5040

1,9,2,8,3,( ),4,6,5,5

2, 3, 6, 8, 8, 4,( ),( )

6. 1/2, 1/5,2/9,3/ 14,5/20,(),( )

7. My brother is older than Xiaoli this year 12 years old. Eight years ago, my brother was four times older than Xiaoli. How old are they this year?

The sum of the ages of Xiaoming's parents is six times that of Xiaoming this year, and five times that of Xiaoming four years later. So what is the total age of Xiaoming's parents this year? If Xiaoming's father is 2 years older than his mother, how old is Xiaoming's father this year?