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| Math Central | Quandaries & Queries |
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Subject: cross multiplication Why does eight over twelve compared to one half work when you use cross multiplication. |
Hi Kayla,
I am going to look at two different fractions. Suppose you want to compare 2/3 and 5/8 to see which is larger. It would be easy to compare them if they had the same denominator so I am going to use a common denominator (in this case 3 
5 = 24).
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Since 16 > 15 you can conclude that
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Now look at the second fractions in the two lines above, and . The denominators are equal and the numerators are the result of cross multiplying 2/3 an 5/8.
I hope this helps,
Penny
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