As a general rule, adverbs should be placed as near as possible to the words they modify.
'The instructor wants the students to quickly solve the puzzle.' is correct

kartikshah wrote:As a general rule, adverbs should be placed as near as possible to the words they modify.
'The instructor wants the students to quickly solve the puzzle.' is correct

NOPE.

"to solve" is an infinitive and nothing should come between "to" and "solve"

So, therefore The instructor wants the students to quickly solve the puzzle. is wrong.

And, The instructor wants the students to solve the puzzle quickly is correct.

If there is no 'to' then you can put adverb and verb closely.

Ex: I frequently walk to the store. >> Correct
He quickly ran towards the bus >> Correct
His friend asked him to quickly run towards the bus >> Incorrect.

@ VK_VINAYAK:
Not splitting infinitives is an old rule of grammar and sometimes it leads to awkward constructions. Moreover, most native speakers of English (American and British) would split infinitives in both - informal and formal - speech and writing, if required.

Consider this example:
"Email and ask him to provide a quote immediately."

By not splitting the infinitive here, we are creating miscues. Does the sentence want to say:

"Email immediately and ask him to provide a quote."

OR

"Email and ask him to immediately provide a quote." ?

By splitting the infinitive, it may become possible, at times, to clear this confusion.

kartikshah wrote:@ VK_VINAYAK:
Not splitting infinitives is an old rule of grammar and sometimes it leads to awkward constructions. Moreover, most native speakers of English (American and British) would split infinitives in both - informal and formal - speech and writing, if required.

Consider this example:
"Email and ask him to provide a quote immediately."

By not splitting the infinitive here, we are creating miscues. Does the sentence want to say:

"Email immediately and ask him to provide a quote."

OR

"Email and ask him to immediately provide a quote." ?

By splitting the infinitive, it may become possible, at times, to clear this confusion.

Most of the time people, even native, do not adhere to grammar while speaking. But, in GMAT, splitting the infinitive is wrong.