Therefore, in the teaching of fractional multiplication, we should pay special attention to let students understand and master.
[Teaching method] In teaching, let students master similar sentences (temporarily called relative sentences), find out the unit "1" from (1), and say the quantitative relationship.
For example, "the number of girls accounts for 5/9 of the class". From "5/9 of the class", we can know that the class number is "1". According to the meaning of fractional multiplication, "5/9 of the number of classes" can be formulated as "5/9 of the number of classes". Because "the number of girls accounts for 5/9 of the class size"
Another example is: "The number of red balls is less than that of white balls 1/5". Under the conditions, take the number of white balls as the comparison standard and take the number of white balls as the unit "1". After 1/5 is removed from the number of white balls, it is the same as the number of red balls, which means that the number of red balls is 60% less than that of white balls. According to "1/5 of the number of white balls", it can be listed as "number of white balls × 1/5". Because this 1/5 means that the number of red balls is less than that of white balls, the number of red balls is less than that of white balls by × 1/5.
[training method]:
1. Find out the relative sentences with quantitative relations.
2. Read the relative sentences repeatedly and find out the number of "1". (1) The kilogram of Chinese cabbage is 2/3 of that of radish. (2) The number of black rabbits is 7/8 of that of white rabbits. (3) The number of boys is 1/7. (4) Girls are 65438+ less than boys.
3. Draw a line graph according to the relational sentence.
4. Write the quantitative relationship. take exercise
1. Which quantity in the following questions should be regarded as the unit "1", and write the quantitative relationship.
(1) A batch of cement, 2/5 of which was used.
(2) The number of buffalo heads is 5/6 times that of yellow cattle,
(3) Two-thirds of a pile of sand was transported away.
(4) 7/ 10 of b is equivalent to a.
(5) In a book, the number of pages that have been read is 3/4 of the remaining pages.