Scenes of Washington life include pedestrians on the streets with headphones, or cell phones or perhaps a purse. The city’s streets are also home to bicycles and bike riders. And every now and then the pedestrians and the bicyclists do not mix well.

In an example of this, a teenager was arrested Wednesday and charged in four incidents in which a robber on a bicycle rode up to someone in a busy Washington neighborhood, grabbed something and rode away on the same bicycle.

Among the incidents in which the 15-year-old male teenager was charged, police said, was one that happened Feb. 6 in the 600 block of Pennsylvania Avenue SE, near the Eastern Market Metro station on Capitol Hill.

In that incident, police said a robber approached his victim about 8:45 p.m., snatched a purse, and took off on two wheels.

In another of the incidents, police said, someone with headphones was on Massachusetts Avenue NE, near Union Station , just before 7 p.m. on Jan. 28, when a robber approached on a bicycle. The robber grabbed the headphones, police said, and pedaled away.

Three days after that, police said, in the 200 block of 6th Street NE, near Stanton Park, it was about 5;15 p.m. when a robber rode up on a bike. Again, police said, headphones were seized and the robber departed on the bike.

In the fourth incident, police said, it was about 6:30 p.m. in the 600 block of H Street NE on Feb. 11, when a bike-riding robber rode up to someone with a cell phone. The robber took the phone, police said, and made his getaway on the bike.

Obviously not every robbery in the city involves teenagers, or bicycles. But some of them seem unusual in other ways.

For example, in announcing a series of robbery arrests on Sunday, police reported that an arrest was made Wednesday in connection with an incident in which a threat was made and a cell phone was taken Feb. 13 in the 600 block of Kentucky Avenue.

They said the suspect who they arrested was a 12-year-old boy.

Most robbery suspects are men or male teenagers. But a woman was arrested Friday in connection with two robberies, police said. In one of them, police said, money was taken in the 1700 block of H Street NW about 11:20 p.m. by someone claiming to have a pistol.