I have three Led's with forward drop of 1.7 V and 10 milliamp current. I am using 9 V battery with 15 miliamp. I used this website that gave me value of resistor to be used when LED in series or in parallel.

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

For

__3 led in Series__, value is 390 ohms, i.e.

9V-(1.7*3)V/0.01= 390 Ohms

For

__3 LED in 'Parallel'__, it states voltage drop of 243.33 Ohms ??

Can anyone please advise me on what formula i need to use to LED in parallel to derive this value?

I know ampere gets added in parallel...hence i tried 9/(0.01*3)=300 ohms and not 243.33 OHMS..So where I am going wrong..plz advise?