Which one is correct --
The method uses a classifier technique where there are 16 features used.
and
The method uses a classifier technique where there are sixteen features used.
?
Explain why.
Which one is correct --
The method uses a classifier technique where there are 16 features used.
and
The method uses a classifier technique where there are sixteen features used.
?
Explain why.
Both are correct and the meaning is the same. The difference is a matter of style. Many style guides have specific guidelines on when to spell out numbers and when to use digits. If one is writing for an organization that uses a specific style guide, then one should follow that guide's rules or recommendations.
A common guide is to spell out numbers less than 10. However a paragraph in which some values are in digits but others are spelled out is often awkward, and normally all values in a passage should be treated similarly.
The basic rule of thumb - for which there are many exceptions - is that zero to nine is written in words, 10 and above in numbers.
In your example, I think you're pretty unlikely to be judged wrong if you go with 16. I don't think an obvious exception applies here.
A good summary is here, with the caveats being that (a) you should use what makes most sense and reads best in the context and (b) it depends on the specific style guide for the publication you are using.