Question on calculating EV

[thesweetscience]

I was wondering how you calculate your hand's EV against a range of hands. Do you figure the EV of all the hands in the range and then take the average? Is this type of calculation possible? I'm not really sure. Thanks for the help.

[guaranteedBluff]

EV of your hand against each possibility times the probability that this is the hand which your opponent holds.

Example:
(.50) * flush draw EV + (.50) * set = EV

in a situation where 50% of the time you think your opponent has a flush draw and 50% of the time he/she has a flush.