# A substance has a half-life of 3 years. If 2000 grams are present initially, how much will remain after 1.5 years?

$2000 {\left(\frac{1}{2}\right)}^{n}$ n would be time passed in years or number of half lives completed. 1.5 years is 1/2 of the half life so we will put n as 1/2 to get 1414 grams. To sig figs if necessary, 1000g