If a man takes 8 pills, one every 3 hours, how long until all the pills are taken?

To determine how long it takes for the man to take all 8 pills, we need to consider the timing of each pill. If he takes his first pill at time zero, he will take subsequent pills every 3 hours.

He takes the first pill immediately, which counts as hour zero. After that, he will take the following pills as follows:

• 1st pill: 0 hours

• 2nd pill: 3 hours (after the first)

• 3rd pill: 6 hours (after the second)

• 4th pill: 9 hours (after the third)

• 5th pill: 12 hours (after the fourth)

• 6th pill: 15 hours (after the fifth)

• 7th pill: 18 hours (after the sixth)

• 8th pill: 21 hours (after the seventh)

Thus, he takes the 8th pill after 21 hours. The total time until all pills are taken is therefore 21 hours. This calculation shows that the timing is consistent; each pill is taken at 3-hour intervals, and the final pill's timing confirms that 21 hours is indeed the total duration for taking all the pills.