Lipitor, a pharmaceutical drug that has been shown to lower "bad" cholesterol levels while raising "good" cholesterol levels in patients taking the drug, had over $\$ 11$ billion in sales in 2006 . Assuming one $2.5$ -g pill contains $4.0 \%$ of the active ingredient by mass, what mass in $\mathrm{kg}$ of active ingredient is present in one bottle of 100 . pills?
