Lenny can swim 5 laps every 4 min. how many laps can he swim in 15 min?

4 min = 5 laps
15 min = (15 x 5)/4 = 75/4 = 18.75 laps

The rate at which Lenny can swim is equal to the number of laps swam per minute. In this case, the rate is equal to 5 laps per 4 minutes or equal to 1.25 laps per minute. For 15 minutes of swimming, the number of laps then is equal to 1.25 laps per minute * 15 minutes equal to 18.75 laps