00:01
Okay, we have here two points, call them a and b, 30 miles apart on a river, and the current we're saying is flowing from right to left.
00:12
And we're going upstream first, so this way.
00:17
So let's say the current then is equal to c miles per hour.
00:23
And let's say then that the boat in still water is x miles per hour.
00:32
The speed.
00:34
So x miles per hour is still water, no current.
00:41
So going then a to b, we're against the current, we're going upstream.
00:47
So the overall speed will be x minus c.
00:53
When you come back, of course, you're going faster because the speed overall is x plus c.
01:01
The current is helping you.
01:03
So going then upstream would be slower and coming back.
01:07
And we are told that it takes five hours to go upstream.
01:13
Well, speed equals distance divided by time, miles per hour.
01:25
So speed going from a to b, upstream is x minus c.
01:34
Distance is 30...