# Direct and Inverse Proportions

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Two quantities are said to be in direct proportion if:
- the increase in one quantity causes the increase in the other, or
- the decrease in one quantity causes the decrease in the other.

Two quantities x and y are in direct proportion, if x/y = k or x = ky
also, when x and y are in direct proportion, then x1/y1 = x2/ y2
(where y1 and y2 are values of y corresponding to the values of x1 and x2 respectively.)
There are two methods to solve the direct proportion problems: Unitary method and Tabular method.

Two quantities are said to be in inverse proportion if:
- the increase in one quantity causes the decrease in the other, or
- the decrease in one quantity causes the increase in the other.

Proportion is a relation or adaptation of one portion to another, or to the whole, with respect to the magnitude or quantity. In other words, proportion is a harmonic relation between parts, or between different things of the same kind.

Two quantities x and y are said to vary in inverse proportion, if there exists a relation of the type xy=k, where k is a constant.

A constant is a value of any type that can never change. In other words, it always remains same.

Inverse means opposite in nature or effect with another quantity.

Magnitude can be defined as a number assigned to a quantity so that it may be compared with other quantities.

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