Why is "en" necessary in this sentence?

Question

Vi un signo en el baño que decía:

Si usted es el último en salir el baño apague la luz por favor

Is this sentence correct? If so, why is "en" placed before the infinitive "salir"?

Thanks for fixing the ví ... :) - 0066c384, Jun 6, 2011

And the "decia" :) - 0066c384, Jun 6, 2011

Vi has no accent mark, decía does. The último is correct now. - 0074b507, Jun 6, 2011

Thanks, Q! I think it is correct now. I got confused trying to edit. :) - 0066c384, Jun 6, 2011

Answer 1

Because without "en" it would mean "If you are the last exit".

Even in English, you use prepositions after "last", e.g. "last in the competition". If you can use a noun in Spanish, you normally can use an infinitive:

último en la clase

último en entrar

último en salir

último en todo

Thank you. :) - 0066c384, Jun 6, 2011

Good to know! - --Mariana--, Jun 6, 2011