A bell tolls every 10 minutes. Another bell tolls every 15 minutes. Both bells toll at 6:00 PM. They will toll together again at :

I believe the next time both bells will ring at the same time is at 6:30PM.

Step-by-step explanation:

If the bells toll together at 6:00PM, the next time they toll together again should be at 6:30PM.(this is just how it works in my mind) if you add 15 to 15,, you get 30, right? And if you add 10+10=10, you get 30, right? And since 30 is a common number that both 10 and 30 can go into,, and is the lowest number both can go into,, it has to be the answer.

e.

step-by-step explanation:

because there are always 10 numbers in a phone number.