Question 133442
Let {{{c}}}= speed of the current
Let {{{b}}}= speed of the boat
I'm not sure what "210 mi downstream and back" means
I'm assuming it means 105 mi one way and 105 back
(distance traveled against current) = (distance travelled with current)
{{{d = 210/2}}}
{{{d = 105}}}mi
For downstream:
{{{105/10 = 10.5}}} mi/hr
For upstream:
{{{105/70 = 1.5}}}mi/hr
{{{b + c = 10.5}}}
{{{b - c = 1.5}}}
Add these
{{{2b = 12}}}
{{{b = 6}}}mi/hr
{{{b - c = 1.5}}}
{{{6 - c = 1.5}}}
{{{c = 4.5}}}mi/hr
The speed of the boat in still water is 6 mi/hr
The speed of the current is 4.5 mi/hr
check answers:
{{{(b + c)*10 = (b - c)*70}}}
{{{(6 + 4.5)*10 = (6 - 4.5)*70}}}
{{{105 = 105}}}
OK