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Ratio and Proportion


A ratio is a comparison of two numbers. For example, if 25 students -- 10 boys and 15 girls -- are in your class, then the ratio of boys to girls is 10 to 15. A ratio can be expressed in three ways. The ratio of boys to girls in your class might be expressed as

  • 10 to 15
  • 10:15
     
  • 10
    ---
    15
     

More Ratio Resources

* AAA Math
* Algebra Help
* BBC Skillwise
* Get Help with Ratios
* Math.com
* Purple Math

We can use an equation to show that two ratios are equivalents of each other. The proportion can be expressed in two ways:

  • 10:15 = 2:3
     
  • 10   =    2
    ---         ---
    15         3
     

If you want to figure out a ratio that's the equivalent of another ratio, cross multiplying can be used to find the unknown number. For example, cross-multiply (multiply in each direction diagonally) to find the missing number (x) in the proportion below:

8     =     x
---          ---
10         50

 

10 times x is 10x, and 8 times 50 is 400, so we can write this as

 

10x = 400   (this means "10 times what equals 400?")

 

Since 10 x 40 = 400,

 

8     =     40
---           ---
10          50

 

 

Ratio Lesson Plans

Ratio Worksheets

Ratio Interactive Activities

 

Updated 10/13/2013

 

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