Generic LED question

[Sohryu76]

This was posed to me today, and It stuck me... The guy who asked it is an electrical wizard, so I know he has something up his sleeve with the answer.
I already gave him my answer, lets see what you guys say here:

"What would you say if I take 3 LED's rated at 3 volt each, 15ma each, and wire them in parrallel to a 3v coin cell battery?

Or, take those same 3 LED's and wire them in series to a 9v battery?"

What am I missing here?
besides the 3 in parrallel not lasting as long, and being a lil dimmer,
the three in series shouldnt have the one end being dimmer than the other problem, but the one would be warmer than the rest...

there has to be something I'm missing that is easy as cake...

[luis rojas]

You will need 3 resistors in the pararel setup instead of only one with the series setup. Both cases the resistor value will be different.

[Sohryu76]

You will need 3 resistors in the pararel setup instead of only one with the series setup. Both cases the resistor value will be different.

that is not correct except for a technicality.
the voltage of the power sourse equals the voltage of the LEDs in that case...
a 3 Volt LED does not really need a resistor with a 3 volt power supply. and in parallel they are reach getting 3 volts...

in the other option...
the three LEDs together are drawing 9 volts off of a 9 volt power supply.
again a resistor is not needed.