8. Linda goes to visit a friend who lives in Lompoc. It is 390
miles from Linda's house to her friend's house. When she came
back, she didn't stop, so it took her a half an hour less time
and her average speed was 5 miles per hour faster. How fast was
she going when she went down to Lompoc, and how fast was she
going when she drove back? First we define our unknowns. In this
case they are looking for how fast she was driving when she went
down to Lompoc and how fast she was driving when she drove back.
We could set this up with two unknowns, but since we know that
she averaged 5 mi/hr faster coming back we could and then we
would have that Some authors suggest we make up a d = rt table
to organize our thinking. Once we have two columns filled in we
can fill in the third column by using the appropriate form of
the d = rt equation. In this case we need to fill in the column
for the time so we use the equation Now the sentence "It took
her a half hour less time to get back." can be translated as
This gives us a