Cara and Dan race around a running track. Cara runs at a constant rate of one lap every 4 minutes and Dan runs at a constant rate of one lap every 5 minutes. If they both start at the same time, how many minutes will it take for Cara to get exactly one lap ahead of Dan?	Choose one:  A) 18  B) 20  C) 22  D) 24  E) 25
Let x be the number of minutes it takes for Cara to get one lap ahead.   Then Cara ran x/4 laps and Dan ran x/5 laps.   x/4 = 1+x/5   5x=20+4x   x=20   The answer is 20.
<result>B</result>
Cara and Dan race around a running track. Cara runs at a constant rate of one lap every 4 minutes and Dan runs at a constant rate of one lap every 5 minutes. If they both start at the same time, how many minutes will it take for Cara to get exactly one lap ahead of Dan?