If I read the sentence
Find ten apples and oranges.
Do I need to find ten or twenty pieces of fruit?
I think its ambiguous. If the question was:
"Find ten apples and ten oranges." this is no ambiguity.
It is the writer's responsibility to communicate clearly and without ambiguity.
If you have to struggle to determine which of three or four possible questions is actually being asked, it's not YOUR fault, it's his.
And can be both a distributive coordinator and a joint coordinator. So, for example, if a subject includes a distributive and, then the predicate applies equally and distinctly to both noun elements:
John and Mary live in London
John lives in London and Mary lives in London.
A subject including a joint and cannot be expanded in this way. So,
John and Mary are a happy couple
is incoherent as
John is a happy couple and Mary is a happy couple.
Often, however, there is no way to reliably interpret if the and is a distributive coordinator or a joint coordinator. For example:
John made cheese and cucumber sandwiches.
Did all the sandwiches consist of both cheese and cucumber (joint coordination) or did he make cheese sandwiches and also make cucumber sandwiches (distributive coordination)?
The OP's sentence Find ten apples and oranges is ambiguous in the same way.
There is a brief discussion of distributive / joint coordination in The Handbook of English Linguistics (Aarts).
It's like someone saying they "have three brothers and sisters".
Is that a total of six siblings or three? Do they have two brothers and one sister, or two sisters and one brother?
As a result we can read the OP's sentence as
Possible variations which would avoid this ambiguity:
Find ten of each fruit: apples and oranges. (20)
Find ten apples and ten oranges. (20)
Find ten apples or ten oranges. (10)
Find ten fruit which are apples and oranges. (10)
S L Bayer, in ... events and arguments in compositional semantics discusses the different (and sometimes conflicting) usages demanded of 'and'. He concludes that 'ten apples and oranges' (or in his example 'ten men and women') is ambiguous not because some people use 'and' constructions in idiosyncratic ways, but because the ways 'and' is used in 'Standard English' necessarily give rise to alternative interpretations.
An article by L Champollion [top link] has:
...collectively interpreted conjunctions of plural nouns are in principle ambiguous as to the number of entities involved. So five men and women can involve reference to a total of ten people, with five men and five women ... or (more likely) to a total of five people, with some men and some women among them.
The sentence needs rephrasing.