Question

An element with mass 430 grams decays by 27.4% per minute. How much of the element is remaining after 19 minutes, to the nearest 10th of a gram?

Answer 1

The equation for exponential decay is $y=a*b^x$, where a is the initial amount, b = 1 + r (the growth rate as a decimal number) and x is the number of time periods (in this case, minutes).  Substituting the information we have:
$y=430(1+-0.274)^1^9 \\=430(1-0.274)^1^9 \\=430(0.726)^1^9=0.98$.  To the nearest tenth of a gram, this would be 1.0 grams.