Question

An element with mass 780 grams decays by 17.1% per minute. How much of the element is remaining after 19 minutes to the nearest 10th of a gram

Answer 1

Step 1
Formulate a recursive sequence modeling the number of grams after n  minutes.
we have that
100%-17.1%-------------- > 82.9%------------> 0.829

a(n) = 780*[0.829^n]

for n=19 minutes
a(19)=780*[0.829^(19)]=22.1121 g---------------> 22.1 g

the answer is 22.1 g