Expert: Abe Mantell - 1/9/2009

Question
David started across a lake 15 miles wide in his fishing boat at 10 miles per hour. He had to row the rest of the way at only 5 miles per hour after his motor went out.  If he was rowing for half the time that the total trip took, how long did the total trip take?

Answer
Hello Brenda,

Since distance = rate X time, we can set it up as follows:
Let t = the total time the trip took, thus
t/2 = the time he traveled at 10 miles/hr, and
t/2 = the time he traveled at 5 miles/hr.
Thus, the total distance he traveled is
10(t/2) + 5(t/2), i.e. the sum of the distances traveled during each part
but we know the total distance is 15 miles, so...
10(t/2)+5(t/2)=15 ==> 5t+2.5t=15 ==> 7.5t=15 ==> t=2
Thus, he traveled for 2 hrs at 10 miles/hr AND 2 hrs at 5 miles/hr,
for a total time of 4 hrs.

OK?  I hope this helps!

Abe