Teaching objectives:
1, combined with the specific situation, feel the necessity of adding and subtracting fractions of different denominators.
2. Understand the addition and subtraction of different denominator fractions through origami.
3, can correctly calculate the addition and subtraction of fractions with different denominators, and solve the practical problem of simple fraction addition and subtraction.
4. Infiltrate and transform ideas, and cultivate the ability of migration, analogy and induction.
Teaching emphasis: can correctly calculate the addition and subtraction of different denominator fractions.
Teaching difficulty: understanding the addition and subtraction of different denominator fractions.
Teaching preparation: PPT courseware, several rectangular pieces of paper with the same size.
Teaching process:
First, check the import:
1, fill in.
1/2=( )/4=4/( )
2. Find the least common multiple of the following groups.
6 and 8
7 and 14 1 1 and 9
3. Divide the score into the following grades.
1/4 and 3/8 7/ 10 and 5/6
4. Answer first:
1/5+2/5
3/7+2/7 4/9+5/9
5/8-3/8
1 1/ 15— 1 1/ 15 7/ 12—5/ 12
Summary: Add and subtract fractions with denominator, denominator remains unchanged, only numerator is added and subtracted.
Second, explore new knowledge:
1, create a situation.
PPT demonstration: students in handicraft class origami. Naughty with a piece of paper 1/2 fold a boat, laughing with the same piece of paper 1/4 fold a bird.
Teacher: Based on this information, what questions can you ask? Will you solve these problems? (Students list formulas. )
What is their sum (difference) first?
PPT demonstration:
1/2+ 1/4 is between ().
a、0— 1/2 B、 1/2— 1
c、 1—2
2. Try to explore and verify.
Teacher: Is everyone's estimate right? We can verify it by origami.
Display operation tips:
(1) Draw its1/2 on rectangular paper with your favorite color;
(2) Paint its 1/4 with different colors; (Not repeated)
(3) Observe how much these two colors account for this paper.
After the students start the operation, feedback the estimated results. Tell how 3/4 is arrived at.
3. Can the scores of different denominators be added directly?
Communicate at the same table. Summary: For addition with different denominators, divide first, and then calculate according to the method of fractional addition with the same denominator. (blackboard writing)
4. Independent test: 1/2— 1/4. The whole class exchanges the calculation results and methods of fractional subtraction with different denominators.
5. Give it a try:
Finish the textbook "Try it". (3/4+5/8 9/ 10— 1/6)
Complete independently and check at the same table.
6. Summary: How to calculate the addition and subtraction of different denominator scores? (PPT presentation)
Third, consolidate the exercises:
1, topic 1 in the textbook on practice. Let the students consolidate the arithmetic of fractional addition with different denominators. )
2. Question 3 of the textbook "Practice and Practice".
Finish it independently and communicate with the whole class.
Everyone has mastered the addition and subtraction of different denominator fractions. Next, let's be a little teacher and help Ma Xiao to see if his calculation is correct.
2/3+ 1/4=2/ 12+ 1/ 12=3/ 12= 1/4
1 1/ 14—5/7= 1 1—5/ 14—7=6/7
(1) Think independently first.
(2) Who will be the teacher and help him point out the problem?
(3) What advice do you want to give Xiao careless through the practice of this problem?
Next, let's go into the mathematical world of life to solve the problem.
We make a lot of domestic garbage every day, and sanitation workers sort out the garbage generated in our lives and draw the following conclusions:
Scrap metal accounts for1/4 of domestic waste;
Waste paper accounts for 3/10 of domestic waste;
Plastic bags account for 2/5 of domestic garbage;
Other garbage accounts for 1/20 of domestic garbage.
According to this information, what math questions can you ask? And try to solve it.
Fourth, expand and extend:
1. There are three colors of bars, red, yellow and blue. The red bar is 3/4 meters longer than the yellow bar, and the blue bar is 1/6 meters shorter than the yellow bar.
(1) How many meters is the difference between the red stick and the yellow stick?
(2) If the blue bar is1/6m longer than the yellow bar, how many meters is the difference between the red bar and the blue bar?
Guide students to try to solve problems by drawing line segments.
2、( 1) 1/2+ 1/3= 1/3+ 1/4= 1/4+ 1/5= 1/3+ 1/5=
(2) 1/2- 1/3= 1/3- 1/4= 1/4- 1/5= 1/3- 1/5=
A. observation characteristics; B. calculate and find the law; C. give an application example.
Verb (abbreviation of verb) course summary:
1. What did you gain from today's study? Is there a problem?
2. Teacher: Mathematics is everywhere around us. I hope students can use what they have learned today to solve math problems in real life.