As far as I am concerned, DL should not accept "a few books" as a correct answer. "I have few books" = "I don't have many books" while "I have a few books" = "I have some books" (not necessarily few, moreover "quite a few"="many"). So, unless "wenige" covers the latter meaning as well, "a few" should not be accepted.
Thanks for your answer. However, this brings another question:
If the comparative from "weniger" is undeclinable, how do you then distinguish it from "weniger" as a declined form of "wenig". I.e., how do you know whether "weniger Wein" (nominative) means "little wine" or "less wine"? Or, bringing it closer to the example we are discussing here, how would you know whether an instance of "weniger Bücher" in genitive (as in "wegen weniger Bücher") refers to few books or fewer books?
Sorry for being thick, but that still does not help me:
The line just above the one you have circled mentions "wenig" as an uninflected form. Yet it is "wenige Bücher" (as in this exercise). So why is the comparative form "weniger" any different?
(Also, English "uninflected" is an ambiguous word here: it can be uninflected because it's uninflectable or simply because they list the forms that have not been inflected, but can be inflected.)
Checking the entry for Komparativ→Starke Deklination→Plural→Akkusativ: wenigere, which is clearly not what you are saying. Could you please explain the discrepancy?
Here are some examples of weniger being declinable as wenigere for the plural according to these entries in Reverso Context
No, not for several reasons:
Firstly, "less" is a comparative form, meaning that the quantity is smaller than some other quantity, specified directly or implied. The German analogue would be "weniger" (instead of "wenig") or, in this particular instance, "... wenigere Bücher".
Secondly, "less" is the wrong comparative form for countable objects such as books. You would have to use "fewer books" instead. Now, that rule is being constantly eroded in colloquial speech, at least in the US where is not uncommon to see supermarket signs "10 items or less", but it's still wrong.