When solving problems on proportions is always possible to use the same principle. That they are comfortable. When dealing with proportion, always proceed as follows:Define the unknown and label it with the letter H.
Record the condition of tasks as a table.
Determine the type of dependence. They can be direct or reverse. How to determine the type? If the proportion is subject to the rule "the more, the better", so a direct relationship. If on the contrary, "the more, the less", it means an inverse relationship.
Put your hands with the edges of the table in accordance with the type of dependency. Remember: the arrow pointing upwards.
Using the table, write a proportion.
Solve the proportion.
Now let us examine two examples of different types of dependence.Task 1. 8 yards of cloth cost 30 R. How much are the 16 yards of this cloth?
1) the Unknown - the cost of 16 yards of cloth. Let's denote it as x.
2) let's Make the table:8 yards 30 p.
16 yards x R. 3) to Define the type of dependency. Think: the more cloth you buy, the more you will pay. Therefore, a direct relationship.4) Put the arrow in the table:^ 8 yards 30 p. ^
| 16 yards R. x |5) we form the ratio:8/16=30/xx=60 p answer: the cost of 16 yards of cloth is 60 p.
Task 2. The motorist noticed that at a speed of 60 km/h he drove a bridge across the river for 40 s. On the way back he passed the bridge in 30 s. Determine the speed of the car on the way back.1) the Unknown - the speed of the car on the way back.2) let's Make the table:60km/h 40
x km/h 30 C3) Define the type of dependency. The greater the speed, the faster a motorist will pass a bridge. Hence the inverse relationship.4) will form the proportion. In the case of inverse relationship here a little trick: one of the table columns you need to flip. In our case, we get the following proportion:60/x=30/40x=80 km/cotvet: back on the bridge a motorist drove at speeds of 80 km/h.