Trisha
I always advise students to substitute easier numbers into these kinds of problems as a way to see how to solve them.
The first girl runs 2 1/2 laps in 15 minutes. What if instead she ran 2 laps in 10 minutes, how many minutes did it take her to run 1 lap? Easy to see it took 5 minutes right? She ran 1 lap for 5 minutes, and the 2nd lap for another 5 minutes, total 10 minutes.
So your ratio is 10/2, in other words you want the time it took her to run the laps divided by the number of laps.
The true number for Kristi is then 15 divided by 2 1/2. In this case you can do 15/2.5 = 6, that is she runs a 6 minute lap.
The other girl runs 1/2 laps in 3 1/2 minute. Again what if she runs 1/2 lap in 3 minutes what would you say her time was for 1 lap? Twice 3 minutes right? So this one is easy, it is twice 3 1/2 minutes or 7 minutes. You could also have done the same as above, divide the time by the distance for 3 1/2 divided by 1/2 or 3.5/.5 = 7
The first girl, Kristi, runs faster.
All the best
Lori
