A proportion is simply a statement that two ratios are equal. ... In problems involving proportions, we can use cross products to test whether two ratios are equal and form a proportion. To find the cross products of a proportion, we multiply the outer terms, called the extremes, and the middle terms, called the means. Kinds of proportion :
Direct Proportions/Variations
Two values x and y are directly proportional to each other when the ratio x : y or  is a constant (i.e. always remains the same). This would mean that x and y will either increase together or decrease together by an amount that would not change the ratio.
Knowing that the ratio does not change allows you to form an equation to find the value of an unknown variable.
Inverse Proportions/Variations or Indirect Proportions
Two values x and y are inversely proportional to each other when their product xy is a constant (always remains the same). This means that whenx increases y will decrease, and vice versa, by an amount such that xy remains the same.
Knowing that the product does not change also allows you to form an equation to find the value of an unknown variable.
For more info :
0 Comments