Maths

[Guest]

I go for a walk in the forest every 12 days my friend goes for a walk in the forest every 15 days. Today we both went together , how many days till we walk together again?

[HallsofIvy]

12= 3*4
15= 3*5

The "least common multiple" of 12 and 15 is 3*4*5= 60. You will walk on the same day in 60 days.

Same idea but more basic and more tedious-
Your friend will walk on days 15, 30, 45, 60, 75,...
You will walk on days 12, 24, 36, 48, 60, 72, ...