One in 10 people is or are?

victoVarying opinions on this: Is it 'one in ten people is' or 'One in ten people are'?

It's are.

With fractions and percents the verb agrees with the noun that follows in the of-phrase.

An expression like "one in ten people" is not a statement about one person, so it's not a question of "one is".
Instead, the expression is

Thanks, CJ. This is a big dispute - and your explanation makes perfect sense.

victoThis is a big dispute

Life lesson.
Like most big disputes, it's a dispute over something small.

What about 'One in ten pies were consumed'?

'Only one out of ten pies was consumed'. ?

victoOne in ten pies were consumed / Only one [in / out of] ten pies were consumed.

Fractional meaning. OK as is. There may have been hundreds of pies. One tenth of them were consumed.

victoOnly one out of ten pies was consumed

Non-fractional meaning. There were ten pies to start with, and one was consumed, leaving nine.

'Only one out of ten pies was consumed'.

Because 'only' is referring to just one pie, is the verb 'was' in this sentence?

victoBecause 'only' us referring to just one pie, is the verb 'was' in this sentence?

No. You can also use 'only' with the fractional meaning, which I already added for you as an illustration (in the first quote box in my previous post).

CJ

I found this lengthy thread very interesting:

http://ask.metafilter.com/197593/1-in-10-kids-is-or-are

A good topic indeed!

MFGlengthy thread

You can say that again!

MFGvery interesting

Opinions will vary about how interesting it is.