Video narration
How long does the boat take to travel 16 kilometers downstream and then 16 kilometers back upstream? The boat moves at 8 km/h in still water, while the river current is 4 km/h. Because the current helps the boat downstream, add the speeds: 8 plus 4 equals 12 km/h. Now, going upstream, the current works against the boat, so subtract it: 8 minus 4 equals 4 km/h. For each part, use time equals distance divided by speed. Downstream, the time is 16 divided by 12, which is 4 over 3 hours, or 1 hour 20 minutes. Upstream, it is 16 divided by 4, giving 4 hours. Add the two travel times: 1 hour 20 minutes plus 4 hours equals 5 hours 20 minutes. So, how long is the complete round trip? The boat takes 5 hours 20 minutes.