If we were just talking about numbers, any numbers (whole, fractions, decimals, positive, negative) could be used. But since we are talking about actual living objects, we can only use whole positive. The simple way to look at this is if there are 3 tulips, how many daisies would there be? The answer is, of course, 5. So the total number of both would be 8. So since the ratio is always of whole numbers, the answer would be some multiple of 8.
For example, 80 flowers would have 30 tulips and 50 daisies. (30:50 is the same as 3:5)
