Respuesta :
well, keeping in mind, the boat's speed is still water is 32mph
now, when the boat goes upstream, is not really going 32mph, is going slower, because the river stream is eroding speed from it, let's say the stream rate is "r" fast, so the boat is going upstream at 32 - r
and when going downstream, it goes "with" the stream, so the boat is really going faster than 32mph, is going 32 + r
now, recall your d = rt, or distance = rate*time
keep in mind, the time, whatever that is, is the same for the boat in this case, same time going up as going down
thus [tex]\bf \begin{array}{lccclll} &distance&rate&time\\ &-----&-----&-----\\ upstream&72&32-r&t\\ downstream&120&32+r&t \end{array} \\\\\\ \begin{cases} 72=(32-r)t\implies \cfrac{72}{32-r}=\boxed{t}\\\\ 120=(32+r)t\\ ----------\\ 120=(32+r)\left( \boxed{\cfrac{72}{32-r}} \right) \end{cases}[/tex]
solve for "r"
now, when the boat goes upstream, is not really going 32mph, is going slower, because the river stream is eroding speed from it, let's say the stream rate is "r" fast, so the boat is going upstream at 32 - r
and when going downstream, it goes "with" the stream, so the boat is really going faster than 32mph, is going 32 + r
now, recall your d = rt, or distance = rate*time
keep in mind, the time, whatever that is, is the same for the boat in this case, same time going up as going down
thus [tex]\bf \begin{array}{lccclll} &distance&rate&time\\ &-----&-----&-----\\ upstream&72&32-r&t\\ downstream&120&32+r&t \end{array} \\\\\\ \begin{cases} 72=(32-r)t\implies \cfrac{72}{32-r}=\boxed{t}\\\\ 120=(32+r)t\\ ----------\\ 120=(32+r)\left( \boxed{\cfrac{72}{32-r}} \right) \end{cases}[/tex]
solve for "r"
The speed of the current is 32 mph because a boat in still water is carried by the current.
