Question

Hansen and his good buddy Xavier are both mechanics at a shop that does oil changes. They are in a friendly competition to see who can complete the most oil changes in one day. Hansen has already finished 7 oil changes today, and can complete more at a rate of 2 oil changes per hour. Xavier just came on shift, and can finish 3 oil changes every hour. Sometime during the day, the friends will be tied, with the same number of oil changes completed. How many oil changes will Hansen and Xavier each have done? How long will that take?

Answer 1

Least Common Multiple (LCM)
2: ( already starts at 7)
9, 11, 13, 15, 17, 19, 21
3: 7th hour
3, 6, 9, 12, 15, 18, 21
7th hour

At the 7th hour, they both have done 21 oil changes.