Mark goes to the mall every 4 days, costco every 2 days, and the grocery store every 3 days. if he goes to all three on the 15th, when will he go to all three again?

Mark will go to all three again on the 27th.

You must find the least common multiple of 4, 2, and 3. That is, find the smallest number that is divisible by all three of the numbers. You get 12. 12 is divisible by 4, 2, and 3.

Finally, add 12 to the 15th to get the 27th.