Fun with Grammar!

Remember School House Rock? I do not recall one on subject-verb agreement but there should be. If one rule of grammar is broken more often than any other, this is the one.

I saw a billboard yesterday that said "1 in 5 children is sexually exploited on line." Here is my photoshop version of it:

Now, aside from the serious but unproveable message, do the subject and verb agree?

The question becomes "Who is the subject of the sentence?" Is it "1"? If so, then the subject-verb matches. "1 is sexually exploited on line."

But isn't "1 in 5" a modifier of "children"? If the term "twenty-percent of" were substituted in place of "1in 5" then the subject-verb would be "twenty-percent of children is..."

So what is the grammar rule?

Rule 9.
With words that indicate portions—percent, fraction, part, majority, some, all, none, remainder, and so forth —look at the noun in your of phrase (object of the preposition) to determine whether to use a singular or plural verb. If the object of the preposition is singular, use a singular verb. If the object of the preposition is plural, use a plural verb.

Examples:
Fifty percent of the pie has disappeared.Pie is the object of the preposition of.
Fifty percent of the pies have disappeared.Pies is the object of the preposition.
One-third of the city is unemployed.
One-third of the people are unemployed.
NOTE: Hyphenate all spelled-out fractions.
All of the pie is gone.
All of the pies are gone.
Some of the pie is missing.
Some of the pies are missing.

So, the object of the preposition is "children" and this billboard should have used the word "are" and not "is". "1 in 5 children are sexually exploited on line"

I knew it looked wrong when I read it. In more ways than one.