did you try drawing a chart to see a picture of what's going on?
Originally Posted by sarahh
the | represents the hours.
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<---> represent the number of hours it can be divided into. there are 12 hours here. in the first line, you see three <---> symbols, that span 4 of the hours at a time. we see that it takes 3 of these symbols to span the 12 hours.
in the second line, there are 2 <--> symbols each spanning 6 hours at a time. we see that the arrow heads line up at the beginning when we have zero hours (when the person just takes the pills) and again at the end of 12 hours (the next time the person takes the two pills together).
so we had to find a number where both 6 and 4 divide into at the same time, because at these numbers, the arrow heads will line up as you see. since we wanted the very next time the arrow heads line up, we wanted the LCM