Question 66549
Use cross products to determine whether each of pair of ratios forms a proportion:

4/9, 12/27
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You are checking the following equality:
(4/9)=(12/27)
You do this by cross multiplying as follows:
4*27=108
9*12=108
Since the cross-products are equal the ratios are equal 
and they form a proportion.
Cheers,
Stan H.