2. One third of the number A is equal to two fifths of the number B, so the ratio between the number A and the number B is (6: 5 = 2 * 3/5), and the number A is one third of the number B, so the ratio between the number A and the number B is (4: 3).

3. In a proportion, two external terms are reciprocal, one internal term is the smallest prime number, and the other internal term is ().

Solve the problem (by proportional method, the calculation process is explained in detail)

Because the product of two external terms = 1, one internal term is the minimum prime number 2, so the other internal term is 1/2, which is proportional to "the product of two external terms equals the product of two internal terms", so the two internal terms are reciprocal.

A clothing factory wanted to produce 2400 shirts, and it finished 40% in the first three days. According to this calculation, how many days will it take to complete these tasks?

3/40%=30/4=7.5≈8 days

Xiaoming's family has built a new house and is ready to decorate it. If you use a square brick with a side length of 50 cm, it will cost 20 yuan. If you change it into a square brick with a side length of 8 cm, how many pieces do you need?

50 * 20/80 = 25/2 ≈ 13

6. For a cup of sugar water, the ratio of sugar to water is 1:9. If the sugar water weighs 52 grams after adding 2 grams of sugar, how many grams of water is there in this cup of sugar water?

(52-2) * 9/( 1+9) = 45g

7. A factory has a batch of coal. It was originally planned to burn 15 tons per day, which can last for 40 days. Actually, it saves 5 tons per day than originally planned. How many days can this batch of coal burn? (Proportional solution)

Solution: When the total amount is fixed, the daily dosage is inversely proportional to the number of days of use.

40 * 15/( 15-5) = 60 days.

8. A pesticide, made from pharmaceutical industry and water in the ratio of 1: 1500, contains 54 kilograms of water. How many kilograms of liquid medicine does it take to prepare this pesticide?

54 * 1/500 = 0. 128kg

Do the math.

5/6 times (3/8+6/ 1X3/ 10)

=5/6X3/8+5/6X 18/ 10

=5/ 16+3/2

=29/ 16

Solution ratio.

x- 2/5x=3/20

3*5x=20*(x-2)

15x=20x-40

5x=40

x=8