I can not figure out these two word problems:

A restaurant has two neon signs. Both are turned on at the same time and both blink as soon as turned on. One sign blinks every 9 seconds and the other blinks every 15 seconds. In how many seconds will they both blink together again?

The school cafeteria serves pizza every sixth day and applesauce every eighth day. If pizza and applesauce are both on today's menu, in how many days will they be served together on the menu again?

And if you can explain how you did it, I will be very grateful!

OK problem number 1. Create your sequence of 9s such as 9, 18, 27,36,45, 54, 63, 72... now do the same for 15s Where do the two sequences match up again? Problem #2 create sequences for both 6 and 9. At what point do they match up.

Thank you so much!! I knew there was a simple way to figure it out, but I just couldn't think straight tonight. This fifth grade math is kicking this mom's butt! Thanks again.

LOL you should see what the kids are tomorrow.

It's a Least Common Multiple problem:

With pictures: Factoring - Least Common Multiple (LCM) - First Glance