How often does the No. 1 bus run?

W: Hi, John. What are you doing here?
M: I’m waiting for the bus.
W: Where are you going?
M: I’m going to the station to meet my sister.
W: Oh, is she coming by herself?
M: Yes, the train comes in about half past four, but it’s twenty past four now. I have only ten minutes!
W: How often does the bus run?
M: Every ten minutes. I missed a No. 1 bus 15 minutes ago, and the next one hasn’t come yet!