Question 1719
ok...first define speed of boat in still water to be v (or whatever letter you want).

downstream, its speed is v+6. Upstream, its speed is v-6.

Now, speed = distance/time, so:

downstream: {{{(v+6)=(92)/t}}}
upstream:   {{{(v-6)=(46)/t}}}

Re-arranging these 2 and equating for t, gives:

{{{(92)/(v+6) = (46)/(v-6)}}}

Re-arranging again gives v=18mph

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2. using speed=distance/time as a start, where distance, d, is the area covered really...

speed of martha = d/2
speed of brother = d/3

together, their speed is {{{(d/2) + (d/3)}}}, and they cover the same space..the yard, so distance is still d...just need to find the time...

{{{(d/2) + (d/3) = (d/t)}}}

cancel the d's gives...

{{{(1/2) + (1/3) = (1/t)}}}, giving

{{{(5/6) = (1/t)}}}

or {{{t = (6/5)}}} hours.

So, hopefully, you have misread the answer. Alternatively, I have the answer wrong!!!




cheers
Jon.