Number ofhalf-liveselapsed Fractionremaining Percentageremaining 0 1/1 100 1 1/2 50 2 1/4 25 3 1/8 12 .5 4 1/16 6 .25 5 1/32 3 .125 6 1/64 1 .563 7 1/128 0 .781 ... ... ... n 1/2n 100/2n Half-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms (radioactive decay), but may apply to any quantity which follows a set-r… (More on Half-life)