Duty cycle question ?

If i knew an led drawed 10ma switched on during 10 sec period how would i calculate how much it would draw at 100hz 50 duty cycle ?

If you are using the same power supply, and the same current limiting resistor as when driving the LED at 100% duty cycle (always on), then if you reduce the duty cycle to 50% (at any chopping frequency) , the power dissipation in the both the resistor and the LED will be cut by 50/100 = 1/2

The brightness will also be reduced to about half (the same as if it used half the continuous current).
That is how an efficient light dimmer works.