A chemical decays in such a way that the amount left at the end of each week is 30% less the the amount at the beginning of that same week. What percent of the original amount is left after 3 weeks?

Alright, let’s start with week 1. At the beginning, you have 100%. At the end, we have to subtract 30% to get 70%.

Summary of week 1

Beginning: 100%

End: 70%


Let’s do week 2, now. We have to start with the end of week 1, which is 70%. By the end, we have to subtract another 30% to get 40%

Summary of week 2

Beginning: 70%

End: 40%

Finally, let’s do the third week. We start with 40% of the original liquid, but, by the end we have to subtract 30% again to get 10%


Summary of week 3

Beginning: 40%

End: 10%

So, we have found our answer! 10% of the original amount is left after 3 weeks.


Hope this helped! Comment if you have any questions!!! :)