Hi pablo, regaring 1) TeX assumes that each character is a variable on math
mode. You need to tell it that each "word" is, well, a "word":

\starttext
  \startitemize[packed]
  \item Valor actual neto: $\text{\em beneficios} - \text{\em costes}$. %
you can use typographical variations inside \text: \em, \bf, etc
  \item Beneficio por euro: $\frac{\text{\em beneficios}}{\text{\em
costes}}$.
  \item Beneficio obtenido el primer año.
  \stopitemize
\stoptext

2) will solve itself ather this. 3, I don't know.



-- 
Andrés Conrado Montoya
Andi Kú
andresconrado@gmail.com
http://sesentaycuatro.com
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http://chiquitico.org
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Los fines no justifican los medios, porque la medida verdadera de nuestro
carácter está dada por los medios que estamos dispuestos a utilizar, no por
los fines que proclamamos.
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“You develop an instant global consciousness, a people orientation, an
intense dissatisfaction with the state of the world, and a compulsion to do
something about it. From out there on the moon, international politics look
so petty. You want to grab a politician by the scruff of the neck and drag
him a quarter of a million miles out and say, ‘Look at that, you son of a
bitch.’” — Apollo 14 astronaut Edgar Mitchell