This one is deceiving my simple. Start with the ratio 2/3. To find more ratios that are proportionate, simply multiply the numerator and denominator by the same number. Let's go with 2. So, 2*2/2*3 (which is 4/6) should be equal to 2/3. If you plug both into a calculator, you will see that they both equal 0.667, and are therefore proportionate.
Here are some more examples:
2/3, 4/6, 6/9, 8/12, 10/15
