Three friends-whose walking rates are 1 ft./sec., 3ft./sec.,and 6ft./sec. start together walking in the same direction around a circular track that is 420 feet in circumference.After how many minutes are the three of them together again?  Choose the correct answer.
A) 5 mins  B) 10 mins  C) 15 mins  D) 3 mins  E) 7 mins
The time they take will be what the 1st friend takes to complete one circumference as he is the slowest and that is the point all 3 of them will be together at the end of 7 mins.   7 mins
<result>E</result>
Three friends-whose walking rates are 1 ft./sec., 3ft./sec.,and 6ft./sec. start together walking in the same direction around a circular track that is 420 feet in circumference.After how many minutes are the three of them together again?