One (1) is singular – it´s obvious, you say. Please consider the following:
- One in ten workers in Tenerife are lazy.
- One in ten workers in Tenerife is lazy.
- One in four politicians in Spain are corrupt
- One in four politicians in Spain is corrupt.
The sentences that use “is” are correct. “One” is singular – how could it be otherwise (no puede ser de otra manera)?
Just because the words politicians and workers are close to the verb does not make them the subject of the sentence. “One” is third person (la tercera persona). End of story (asunto concluido).
The same is true for “per cent”. Consider these:
- 25 per cent of all teachers are incompetent.
- 25 per cent of all teachers is incompetent.
25% is more than 1% so it must be plural, some might say. No. Think again. The version with “is” is correct. Why? Because the sentence is a shortened version of:
- The sum (suma) of 25% of teachers is incompetent.
The sum (suma, importe) is a singular concept and the subject of the sentence – 25% is just more detail. So put on your thinking cap (se estruja el celebro) and consider the following:
- 30,000 pounds is a lot of money.
- 30,000 pounds are a lot of money.
The correct version? 30,000 pounds is a lot of money, because this sentence is a shortened version of: the sum of 30,000 pounds is a lot of money.
A quantity is usually treated as singular (la cantidad es singular en español tambien) as in this example:
“The quantity of two bottles of brandy is required to make the punch (ponche)”.
So enjoy your singular drink of two bottles!