since cpu can process one character in 100 msec, and user is typing at 1 charsec, we can drop the cpu clock speed to 1 sec100 msec110 of its original value in this scenario, which means an optimal value of n10 in this case if the energy consumed in 1 sec at full speed is e, then running at full speed for 100 msec then going idle for 900 msec uses e10 running at 110 speed for a whole second uses e100, a saving of 9e100 the percent savings by cutting the voltage is 90