Question

What two ratios are equivalent to 5:9

Answer 1

There is infinitely many ratios which are equivalent to 5:9. As we know always we can write divide as fraction, so $\frac{5}{9}$. We can multiply nominator and denominator by the any number (but the same) and get another numbers but ratio will be the same, so equivalent.
For example
10:18,
15:27 

Answer 2

The answer is 10:18 because 5x2=10 and 9x2=18