Question 411179
The distance is the same going both ways
upstream:
{{{d = (s - 3)*(3/4)}}}
{{{d = (3/4)*s - 9/4}}}
---------------
downstream:
{{{d = (s + 3)*(1/2)}}}
{{{d = (1/2)*s + 3/2}}}
---------------
{{{(3/4)*s - 9/4 = (1/2)*s + 3/2}}}
{{{(1/4)*s = 9/4 + 6/4}}}
{{{(1/4)*s = 15/4}}}
{{{s = 15}}}
Her boat speed was 15 mi/hr
check answer:
{{{d = (15 - 3)*(3/4)}}}
{{{d = 9}}} mi
{{{d = (s + 3)*(1/2)}}}
{{{d = (15 + 3)*(1/2)}}}
{{{d = 9}}} mi
OK