First, correctly finding the unit "1" is the premise to solve the problem of score application.
No matter what kind of fractional application problem it is, there must be a unit "1" in the problem. Finding the unit "1" correctly is the premise and primary task to solve the problem of fractional application.
The unit "1" in the problem of fractional application appears in two forms:
1, clearly marked:
(1) The number of boys accounts for 4/7 of the class. (2) The number of poplars is 3/5 of that of willows. (3) Xiaoming's weight is equivalent to his father's 1/2. (4) There are more apple trees than pear trees 1/5.
Among the conditions of "accounting", "yes" and "equivalent", the quantity before the score is the unit "1" in this question.
2. No obvious signs:
(1) A road has been repaired for 200 meters, and 2/3 of it has not been repaired. How many kilometers is this road?
(2) 200 sheets of paper, first use 1/4, second use 1/5. Two * *, how many were used? (3) The typist typed a 5000-word manuscript and typed 3/ 10. How many words are left? The unit "1" in these three questions has no obvious mark, so it should be judged comprehensively according to the questions and conditions. In (1), "the total length of a road" should be regarded as the unit "1"; (2) "200 sheets of paper" shall be regarded as the unit "1"; (3) "5000 words" should be regarded as the unit "1".
Second, finding the correct correspondence is the key to solving the problem of fractional application.
Every fractional application problem has a corresponding relationship between quantity and fraction, and correctly finding out which fraction (or quantity) corresponds to the required quantity (or fraction) is the key to solving fractional application problems.
1, draw a line segment to find the corresponding relationship.
(1) There are 12 ducks and 4 geese in the pond. What is the number of geese? (2) There are 12 ducks in the pond, and the number of geese is 1/3 of that of ducks. How many geese are there in the pond? (3) There are four geese in the pond, which is exactly 1/3 of the number of ducks. How many ducks are there in the pond? Show the relationship between these three problems with a line chart. As can be seen from the figure, drawing a line segment diagram is an effective means to find the corresponding relationship correctly. Line drawing can help students understand the quantitative relationship, and at the same time can draw the following quantitative relationship:
The amount corresponding to the score ÷ the amount of the unit "1" = the amount of the unit "1" × the score = the amount corresponding to the score ÷ the score = the amount of the unit "1" 2. Find the corresponding relationship from the conditions in the question.
A bucket of water is 1/4, which is exactly 10g. How much does this bucket of water weigh? 3/4 of water =10.
Third, according to the quantitative relationship, the "three-step method" to solve the problem of score application.
Mastering the above relationship and quantity relationship, solving the application problem of fractions can be carried out in the following three steps: 1, and finding the quantity of the unit "1"; 2. Identify the correspondence 3. Solve problems according to quantitative relations.
Fourth, practice effectively, build a model and improve the ability to solve fractional application problems.
In order to solve the problem of fractional application correctly and quickly, we must practice more and understand the basic, slightly complicated and complicated structural features clearly, so as to solve the problem of fractional application skillfully and quickly.