My math was a little off. at the 50ng after 5 days you would have 25ng of thc in your system, after another 5 days you would have 12.5ng of thc iin your system, after another 5 days you would have 6.25ng of thc in your system, after another 5 days you would have 3.125ng of thc in your system. Hope this was helpful.