Every 3 Days Marco fills up his car with gas. Every 8 Days he washes it. On what day will he fill his car and wash it

Okay. So to answer this question, let’s find the LCM of both numbers, which means listing the numbers that a number can go into evenly.

3: 3, 6, 9, 12, 15, 18, 21, 24, 27

8: 8, 16, 24, 32, 40

When you look at both of them, you see that they both have a multiple of 23. So Marco will fill his car with gas and wash his car on the 24th day.