# 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.

ExampleConsider 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. 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.

ExampleConsider 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.

• Neeraj chak

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?

• MAANSI

IDK{I DON'T KNOW}

• Prashant

It is a case of direct proportion.
Therefore, 16\320 = x\ 1280
X= 16 * 1280 \320
X = 64
Hence 64 people will be needed .

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