Solving Proportions

A proportion is an equation stating that two ratios are equal (two equivalent fractions)

2 sextos 0

Finding the missing value in a proportion means finding the missing value for two equivalent fractions.

There are three ways to solve proportions

Method 1: Vertical

2 sextos 1Since 2 x 3 = 6, then 10 x 3 = 30. So the missing value is 30.

Method 2: Horizontal

 2 sextos 2Since 2 x 5 = 10, then 6 x 5 = 30. So the missing value is 30.

Method 3: Cross-products

2 sextos 3

Cross multiply and solve for X.

The missing value is 30.

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Solving Proportions by Cross Multiplication

In an proportional relationship such as

cross

 

 

 

we can multiply the numerator of each side by the denominator of the other side.

crossmul

 

 

The cross products of a proportion are equal. This property help us solve for an unknown value.

Solving proportions worksheets with an unknown variable  (using only integers):

MKY2

Solving proportions worksheets with an unknown variable  (with one decimal):

MKY2

If one term of a proportion is not known, we can use cross multiplication to find its value.