Algebra homework help

Question

The current of a river is 2 miles per hour. A boat travels to a point 15 miles upstream and back in 4 hours. What is the speed of the boat in still water?

Answer 1

2(15)/4 =30/4 = 7.5 mph in still water, which is very close to the actual speed = 8 mph

It went 30 miles total in 4 hours. just divide 30 by 4

It went 7.5 plus 2 in one direction and 7.5-2 in the other direction

d=rt, distance = speed times time

15/9.5 one way, 15/5.5 the other way

15/9.5 + 15.5/5.5 = 4 hours

1/1.1 + 1/1.9 = 4/3

slower upstream, faster down stream, but they average out to 7.5 mph

you could have made the stream speed any number, and you'd still get the same 7.5 mph in still water.

the stream speed was an annoying distraction

but actually the "average" is slightly different, not 7.5 but 8

distance over speed =

15/(r+2) + 15/(r-2) = 4

4(r^2 - 4) = 15(r-2) + 15(r+2)

2r^2 -15r - 8 = 0

r = 32/4 = 8

Answer 2

[15 / (b - 5)] + [15 / (b + 50] = 4

Can you solve for b and answer?