19. A drug has a blood plasma concentration of 20 mcg/mL. Ten hours later, the plasma concentration is 5 mcg/mL. This drug has a half-life of
hours.

Scientists often deal with numbers that are either very large or very small. for example, the radius of the sun is approximately 696,000 kilometers, while bacterial cells are as small as 1.9 × 10-4 millimeters. express each of these numbers in an alternate form.