One in ten Americans “think” or “thinks”? [duplicate]

I wonder when actor is a 3rd person singular number in this sentence, verb should be ending with the suffix -s or -es or not.

Whats the rule?

Both a singular and plural verb are possible.

One {in ten Americans} thinks that ... Here "in 10 Americans" is a non-defining adjectival phrase modifying the subject "One". This is based upon taking a random sample of any 10 Americans of whom one individual "thinks that..."

{One in ten Americans} think that ... Here "in 10 Americans" is a defining adjectival phrase modifying the subject "One", and the subject is "One in ten Americans" which is a numerous group of about 30 million.

[One in ten Americans] think(s) HTML is a sexually transmitted disease.

The head of the bracketed NP is the plural "Americans", so the simple agreement rule would suggest that plural "think" is correct.

However, the verb can be singular as well as plural, the optional singular override probably being motivated by the presence of "one".

Edit: For those interested in the syntax, "one in ten" is a DP (determinative phrase) in which the PP "in ten" is in post-head modifier function. The DP functions as determiner in the NP subject "one in ten Americans", whose head is "Americans".