Question 1198761
<font color=black size=3>
30 = 6*5
42 = 6*7
GCF of 30 and 42 is 6, since this is the largest factor they have in common.


LCM of 30 and 42 is 30*42/GCF = 30*42/6 = 210


We can verify that with these lists of multiples.<ul><li>multiples of 30: 30, 60, 90, 120, 150, 180, <font color=red>210</font>, 240, 270, ...</li><li>multiples of 42: 42, 84, 126, 168, <font color=red>210</font>, 252, 294, 336, 378, ...</li></ul>I've marked the LCM in red.
This is the smallest common multiple.


The LCM is useful for problems such as this because Linda and Deepti will complete a circuit at the same time every 210 minutes.


Extra info:
210 minutes = 180 minutes + 30 minutes
210 minutes = (180/60 hours) + 30 minutes
210 minutes = 3 hours + 30 minutes
also,
210 minutes = (210/60) hours
210 minutes = 3.5 hours
</font>