There are two bicycle riders travelling towards each other, each travelling at 10Km/hr and the distance between them is 60km. There is also a butterfly that is flying back and forth at 20km/hr between the two riders until it is finally crushed when both riders meet at the mid-point.

Question:

- what is the
**time duration** of the butterflies **second last lag** (i.e. flying from rider 1 to rider 2)? - what is the
**time duration** of the butterflies **last lag** (i.e. flying back to rider 1 where it meets its DEATH) - Is there a simple formula of working this out?

Appreciate the help