# a basic question about getting the value of a parameter [closed]

i am new with Mathematica. i am trying to write a simple code.

for example:

phiu = 2

Yfu = (phi_u/(phi_u + 17.18))


but when i run it, it gives me (phi_u/(phi_u + 17.18)) instead of (2/(2 + 17.18))=0.104275. what can i do to get the value of Yfu?

thank you

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## closed as off-topic by Yves Klett, Sjoerd C. de Vries, Kuba, m_goldberg, Mr.Wizard♦Oct 3 '13 at 12:44

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – Yves Klett, Sjoerd C. de Vries, Kuba, m_goldberg, Mr.Wizard
If this question can be reworded to fit the rules in the help center, please edit the question.

You can't use underscores in variable names. Please lookup the system function Blank[]. –  Sjoerd C. de Vries Oct 3 '13 at 11:04
Also see Pattern –  Mr.Wizard Oct 3 '13 at 12:45

Yfu = (phiu/(phiu + 17.18))