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I. Proportionality tables
1. coefficient of proportionality
Example:
At the market, the reason is sold 3,50€ the kilogram.
For 4 kg, we pay 4 times more than for 1 kg, i.e. 14 €.
Indeed, .
For 0.50 kg, you pay half as much as for 1 kg, i.e. 1.75 €.
Indeed, .
We say that the price, in euros, is proportional to the mass, in kilograms.
The price (in euros) is obtained by multiplying the mass (in kilograms) by 3.5.
In the table above, we go from a number in the first row to the corresponding number
of the second line by multiplying by the same number.
We say that this number (3.5) is a proportionality coefficient (it is the price of one kilogram of grapes).
2. multiplying a quantity by a number
Example 1:
The flow rate of a faucet is regular, i.e. the number of liters flowing is proportional to the duration of the flow. In 5 minutes, 8 liters of water flow out.
How long will it take for 20 L of water to flow out?
So 20 L of tap water will flow out in 12.5 min.
We take example 1 above. In 5 minutes, 8 L of water flows out.
If the tap is left on for 60 minutes, how many liters of water will flow out?
So in 60 minutes, 96 L of water will flow out.
3.additivity of proportionality
Example:
In 5 minutes, 8 L flows out and in 12.5 minutes, 20 L flows out.
min and
L.
So in 17.5 minutes, 28 liters of water will flow out.
II. Passage through the unit and percentage
1. passing through the unit
Example:
With 5 kg of paint, you can cover 8 m² of facade.
- To calculate the surface area of the façade covered with 9 kg of paint, proceed as follows
– with 1 kg of paint, you can cover 8 m²: 5 i.e. 1.6 m².
– with 9 kg of paint, you can cover .
- To calculate the mass of paint required for 30 m² of facade, we can proceed as follows:
-For 1m², you need 5 kg : 8 that is to say 0,625 kg of paint.
– for 30 m², it is necessary .
You can also use this proportionality table:
2.apply a percentage rate
t is a number. To take t % of a quantity is to multiply that quantity by .
Example:
A 125 g yogurt contains 14% fruit.
Calculating the mass of fruit in this yogurt is to take 14% of 125 g, i.e. to take
.
So there are 17.5 g of fruit in this 125 g yogurt.
- Taking 50% of a quantity is taking half.
- Taking 25% of a quantity is taking a quarter.
- Taking 75% of a quantity is taking three-quarters.
Example:
25% of the 28 students in a sixth grade class wear glasses.
so 7 students in this class wear glasses.
Did you learn this course on proportionality and percentages in 6th grade?
QCM de maths sur la proportionnalité et les pourcentages en 6ème.
Skills to learn about proportionality:
- Know the definition;
- Know how to calculate the proportionality coefficient;
- Know how to calculate a fourth proportional;
- Use the cross product;
- Solve problems.
This course is in accordance with the official programs of thenational education.
In addition, you can consult the exercises on proportionality in the sixth grade.
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