Expert: Scott A Wilson - 10/28/2009

Question
many of my teachers disagree with the answer  some say -10  some say-16 What do you think?  Rachel and lisa are swimming laps for a swim meet. They swim at the same constant rate, but Racquel starts swimming before Lisa. When Lisa has finished 2 laps, Rachel has completed 4. How many laps has Rachel completed when Lisa has finished 8 laps?

Answer
R and L are swimmers. When L has 2 laps, R has 4 laps.
Since they swim at the same rate, this means that R had 2 laps when L started
and that R is always 2 laps ahead.

So when L has 8 laps, 8+2 = 10, so R has 10 laps.

If R had swum twice as fast, it would be 2*8, but they swim at the same rate, so it is only 2+8.