00:01
Okay, so a boat on a river travels downstream between two points.
00:05
20 miles apart in one hour, the return trip against the current takes two and a half hours.
00:12
What is the boat speed and how fast is the current in the river flow? okay, so let's label our variables.
00:18
It's the x equal to boat speed.
00:26
And let y equal to our current speed.
00:39
This is our net.
00:42
And then we have also our speed downstream.
00:46
And our speed upstream, which is against the current.
00:54
So we have x minus y, which is equal to the speed against current, and our speed downstream.
01:36
Okay, so we know the boat travels downstream between two points, 20 miles apart.
01:46
So we have downstream, which is x plus y, and that took one hour, which is this 60 over 60.
01:54
That's this one, and that's equal to 12 miles.
01:59
We also have our speed against the current, which is x minus y, and that's two hours and 30 minutes.
02:10
So two hours and 30 minutes.
02:15
Let's make this into a fraction.
02:18
So two times two is four, plus one is five over two...