ANSWER: The heart pumps 24.36 liters of blood in a week.
This type of question can be answered using dimensional analysis, using conversion factors to change units. Units in a fraction must be on opposite sides of the fraction so they cancel themselves out, so if the original fraction has units mL/hour, then the hour must be in the numerator for the conversion factor.
There are 24 hours in a day, and 7 days in a week.
The original fraction is 145 mL/hour. We want to first change hours into days. The hour must be in the numerator of the conversion factor, so our first factor will be 24 hours/1 day.
Now we must cancel out days to leave only weeks as a unit. There are 7 days in a week and there must be days in the numerator, so the conversion factor is 7 days/1 week. We also have to change mL into L. There are 1000 mL in a liter and mL is originally in the numerator, so the conversion factor will be 1 L/1000 mL.
Now we’ll multiply our original fraction by our conversion factors to get out answer with correct units, and we’ll cancel out terms on both the numerator and denominator. Multiply numerators together, and denominators separately.
(145 mL/1 hour) * (24 hours/1 day) * (7 days/1 week) * (1 L/1000mL) = 24.36 L / 1 week. Hours, days, and milliliters have been canceled out because they are all in both the numerator and denominator, so we are left with Liters on top, and weeks on the bottom. There is “1 week” on the bottom, which means that the heart pumps out 24.36 liters of blood per week
