Direct and Inverse Proportions - Class 8 : Notes
1. Direct Proportion:
For any ratio x/y, if on changing the values of x & y, the ratio x/y does not change. Then, we say that x and y are in direct proportion.
In other words, one quantity is a constant multiple of the other quantity i.e. if x = ky where k is a constant. Then, we say that x and y are in direct proportion.
Example:Â Consider the per hour wages paid a company to its employees.
No. of working hours |
Paid Wages (in Rs.) |
1 |
100 |
2 |
200 |
3 |
300 |
4 |
400 |
5 |
500 |
6 |
600 |
7 |
700 |
8 |
800 |
Here, if we consider x as no. of working hours and y as paid wages, then we can find the direct proportion between the two quantities.Â Moreover, the answer of ratio remains same for each case.
If we consider x = 1 and y =100, we get x/y = 1/100.
Now, we consider x = 7 and y = 700, we get x/y = 7/700 = 1/100.
Thus, in any case ratio x/y will remain constant.
2. Inverse Proportion:
For any ratio x/y, if on increasing x by certain amount the quantity y decreases by the same amount. Then, we say that x and y are in inverse proportion.
In other words, if the product of two quantities is constant i.e xy = k where k is constant. Then, we say that x and y are in inverse proportion.
Example:Â Consider the speed and time relationship for five trains to travel same distance.
Train No. |
Speed (in kmph) | Time Taken (in Hrs) |
1 |
25 |
5 |
2 | 50 |
2.5 |
3 |
75 |
1.67 |
4 | 100 |
1.25 |
5 | 125 |
1 |
Here, we can see that as the speed increases the time taken to travel decreases.
Let us consider x as speed and y as time taken.
For train 1, x = 25 and y = 5. So, xy = 125.
For train 4, x = 100 and y = 1.25. So, xy = 125.
Thus, in any case product xy will remain constant.
IF 16 MEN CAN MAKES 320 ART PIECES IN ONE DAY HOW MANY MEN WILL BE NEEDED TO MAKE 1280 SUCH ART PIECES IN ONE DAY?
IDK{I DON'T KNOW}
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