The perimeter of a rectangular window is . If the width of the window is , what is its length?
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Area of bed room = length x width

                             =  4cm x 8cm

                             = 32 cm^2.

You can use the two numbers in the ratio to apply onto a problem. Finding the unit rate helps. 
For example, when you have 3 bananas for every tomato, that means that for each tomato you buy, you buy 3 bananas. When you compare the two, bananas to tomatoes, it can help solve problems.