Question 175111
 Which one of the following statements expresses a true proportion? 1. 2:3 = 3:2 
2. 14:6 = 28:18
3. 3:5 = 12:20
4. 42:7 = 6:2 
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Only #3 does.

Multiply the outsides by the insides (means times extremes).  They have to be equal if it's a proportion.
For #3, 3*20 = 5*12