Respuesta :

1) cross-multiplication: [tex]\frac{x}{y} = \frac{a}{b}[/tex] -> xb = ay

2) common denominator: x/y = a/b -> xb/yb = ya/yb

Cross multiplication is the easiest.

Answer:

cross mulitply and then divide

Step-by-step explanation:

In your proportion you will have 3 of the 4 numbers such as 3/7=9/x.  Mulitply the nubers that are diagonal (cross) from each other.  Here it is the 7 and 9 so 7x9 = 63.  Then you will divide that answer by the number that you haven't used yet, here that is the 3.   So 63/3=21.  x=21.  Works all the time.

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