When purchasing cost will be increased than selling price will be automatically increased, this is called the direct effect.
In same way of effect will be shown when you alone doing some task and taking 4 hrs and if someone join with you and that job done in 1 hr, this is indirectly effect on the job.
If the value of x increases, value of y also increases in such a way that the ratio
x/y does not change; it remains constant (say k). In this case, it is 1/15 (check it!).
We can say that x and y are in direct proportion, if = x/y = k
or x = ky.
So when x and y are in direct proportion, we can write x1/y1 =x2/y2. [ y1, y2 are values of y corresponding to the values x1, x2 of x respectively ]
The symbol for direct proportion is ∞.
If one quantity increases, the other quantity decreases and vice versa such case has to say Inverse proportion to each other.
Thus two quantities x and y are said to vary in inverse proportion, if there exists a relation of the type xy = k between them, k being a constant. If y1, y2 are the values of y corresponding to the values x1, x2 of x respectively then x1y1 = x2y2 (= k), or x1/x2 = y1/y2.
Here we say that x and y are in inverse proportion.
When two quantities x and y are in direct proportion (or vary directly) they are also written as x ∝ y.
When two quantities x and y are in inverse proportion (or vary inversely) they are also written as x ∝ 1/y.