Question 381937
i sailed west to Hawaii against the wind at a speed 12 knots/hour.
 when i returned, i sailed the same route with a wind at a speed of 18 knots/hour.
 what was my average speed for the entire trip? 
:
Let a = average speed for the entire trip
:
Let d = the one way distance
:
Write a time equation: time = dist/speed
:
to time + return time = total time
{{{d/12}}} + {{{d/18}}} = {{{(2d)/a}}}
:
We don't need d, divide thru by d and you have
{{{1/12}}} + {{{1/18}}} = {{{2/a}}}
Multiply by 36a to clear the denominators, results
3a + 2a = 36(2)
:
5a = 72
a = {{{72/5}}}
a = 14.4 knot/hr is the av for the entire trip