Math
posted by Danessa .
One model train travels around a loop every 5 minutes. The other travels on anothe loop every 4 minutes. If they begin at the same point at the same time, how much time will pass before they meet at that point again?

The rate for the first is one loop per 5min, the other one loop per four minutes. The combined rate is the sum of these:
1loop= (lloop/5min + 1loop/4min)*time
time= 1/(1/5 + 1/4) minutes
This is somewhat tricky to get combined, if you wish, you can make decimas..
time= 1/(.2+.25)= 1/.45 and you take it from there. 
200,000=?thousands ? ten thousands ? hundred thousands

time= 1/.45= 2.2 seconds.

oops..time= 2.2 minutes.