Description: Vampires and math students want to know: How many red blood cells are in the a human body? We can find the answer using scientific notation. Created by Sal Khan. A human body has 5 liters of blood, 40% of which is red blood cells. Each red blood cell has a volume of approximately 90 times 10 to the negative 15 liters. How many red blood cells are there in a human body?*Teacher Advisor is 100% free.