Final answer:
To fill a prescription of 3 capsules a day for a week, you multiply 3 by 7, resulting in a total of 21 capsules needed.
Step-by-step explanation:
If a prescription is written for taking 3 capsules a day for 1 week, we need to calculate the total number of capsules required for the entire duration of the prescription. As there are 7 days in a week, we multiply the number of capsules per day by the number of days in a week to get the total.
So, the calculation would be:
3 capsules/day × 7 days/week = 21 capsules
Therefore, the total number of capsules needed to fill the entire prescription is 21 capsules.