total and partial pressure

[oral09]

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I get confused about this, someone clarifies this for me please.
sometime I saw the problem about total pressure and partial pressure they use this formula to solve

P(total) = X (substance A) x P (of substance A)

and sometime I saw them use

P (substance A) = X (substance A) x P total

What did I miss? is this formula for vapor or osmosis pressure?

Thank you

 

[rooney09]

Partial pressure of a A = mole fraction of A x Total Pressure ...this is Dalton's Law

Vapor pressure of solution (solute + solvent) = mole fraction of solvent x pressure of pure solvent....this is Raoult's Law

 

[oral09]

Partial pressure of a A = mole fraction of A x Total Pressure ...this is Dalton's Law

Vapor pressure of solution (solute + solvent) = mole fraction of solvent x pressure of pure solvent....this is Raoult's Law

thanks