Question

Which pair of ratios form a proportion?

3 : 4 and 4 : 5

10 : 12 and 16 : 18

7 : 10 and 10 : 14

5 : 8 and 20 : 32

Answer 1

5:8 and 20:32
If you multiply both 5 and 8 by 4 you get 20:32

Answer 2

5:8 and 20:32 would be a proportion.

Easy way to find this:
Set up the proportion as a fraction.
Use the cross product property. Multiply the diagonals and if the products of the diagonals are the same, then they are proportional.