What is the difference of two positive rational number always positive?

No, while the difference represents the absolute magnitude of two numbers . . . for example . . .

The difference between 5 and 2 is . . . 3
The difference between 6.4 and 9.5 is . . . 3.1

 . . . there is still the chance that the difference may be zero . . . in which case the difference is neither positive nor negative

. . . so in short . . . the answer is . . . NO

11/2.2 = 5 inches for the length 8.5/2.2= 3.86 inches for the width

The answer is biodiversity resulting from new ancestors.