The half life of radon-222 is 3.824 days. After what time will one fourth of a given amount of radon remain?
Decay process. After 7.648 days, you will see one quarter.
From one full unit to one quarter, you need two periods (arrows Show one period or half life). Since half life of radon-222 is 3.824 days, you need twice this time to get one quarter at the end.
You require 7.648 days to reach one quarter at the end.