Translation:The ant is less than ten centimeters long.
If I were asked, "How long is the ant?", then I would just reply, "Ten centimeters.". Adding the "long" clarifies the sentence when it is isolated, like here. The problem I am having is whether I should translate what is written in Portuguese or modify it by throwing extra words like "long" in this sentence, or in a previous one, "five years (old).". Are we trying to translate what is given or polish it up into a dynamic translation? The grading can't distinguish all the possibly correct answers in how we express ourselves so I try for the simplest form. We need to know the philosophy of translation that is being used, if there is any.
Both options are fine.
"De" can be used when it's about numbers.
But "que" is used in comparisons, while "de" is not. Comparisons like "i have less/more than you (have)".
Eu tenho menos/mais que você (right)
Eu tenho menos/mais de você (wrong, unless you mean you are losing/incorporating the features or characteristics of that person in you) - This would mean "I have less/more of/from you".
Eu tenho menos/mais do que você (right)