Baxter waters the lawn every 3 days and mows it every 7 days. He both watered and mowed the lawn July 2. When will he next water and mow on the same day?
Solution
Let us write down all the dates Baxter will water the lawn in July.
July 2: water the lawn
July 5: water the lawn
July 8: water the lawn
July 11: water the lawn
July 14: water the lawn
July 17: water the lawn
July 21: water the lawn
July 24: water the lawn
July 27: water the lawn
July 30: water the lawn
Now, let us write down all the dates he will mow the lawn
July 2: mow the lawn
July 9: mow the lawn
July 16: mow the lawn
July 24 : mow the lawn
July 31 : mow the lawn
After a close examination, we can see that he will water and mow the lawn on July 24.
The method above though is lengthy and time consuming. Is there is quicker way to get the same answer? Yes!
Just get the LCM of 3 and 7
LCM(3,7) = 21
21 days from July 3 will take us to July 24.