Question

A fisherman can

row upstream at
1 mph and
downstream at 4
mph. He started
rowing upstream
until he got tired
and then rowed
downstream to
his starting point.
How far did the
fisherman row if
the entire trip
took 5 hours?

Answer 1

4 [miles].

Explanation:

1) the condition 'the entire trip took 5 hours' can be written as (where t_us - time spent upstream, t_ds - time spent downstream)

`t_(us)+t_(ds)=5;`

2) but the distance [D] upstream is equal the distance downstream, then the condition above can be written:

`(D)/(V_(us)) +(D)/(V_(ds)) =5; \ (V_(us)-rowing \ upstream,V_(ds)-rowing \ downstream);`

3) finally,

`D=(5V_(us)*V_(ds))/(V_(us)+V_(ds));`

D=5*4/5=4 [miles].