math
posted by anthony on .
Solve the problem. A cruise boat travels 48 miles downstream in 3 hours and returns upstream in 6 hours. Find the rate of the stream.

Downstream: 48=(vb+vs)3
upstsream: 46=(vbvs)6
multiply the first equation by 2
1) 96=6vb+6vs
2) 46=6vb6vs
subtract the equations:
50=12vs solve for vs. 
i don't understand the way this is being worded. where did 46 come from? what does vs and vb stand for?

There is a mistake in bobpursley's equations  both should have the same distance of 48.
vs = velocity of stream
vb = velocity of boat
and Distance = Velocity*Time
Downstream
48 = (vb + vs)*3
The stream velocity is +ve as the time is shorter downstream  the stream helps
So vb + vs = 16
Upstream
48 = (vb  vs)*6
The stream velocity is ve as the time is longer so the stream hinders the boat
So vb  vs = 8
Then just solve the 2 equations simultaneously to get vs = 4
Check that and also find the velocity of the boat.
I hope that helps.