"relative to" vs "divided by"
There are a variety of ways you can explain this without using ‘divided by’, and I am not sure ‘relative to’ is particularly good for these cases. I would recommend:
as a proportion of
as it is quite consistent with being equivalent to a decimal value (0.3, 0.9 etc.), whereas relative to seems to me less so (it suggests more a ratio).
e.g
This shows winners as a proportion of total applicants.
This shows adults as a proportion of the total population.
This shows expenses as a proportion of total earnings.