During february, kevin will water his ivy every third day, and water his cactus every fifth day. on which date will kevin first water both plants together?

The answer is the 15th.

If Kevin waters his ivy every third day, and his cactus every fifth day, you want to find the number that can be divided by both 3 and 5. The first day in the month where this can occur is the 15th (which can be divided by both numbers).

The answer is the first one