## Task 3 - 020523

Petra is playing a game of chess with Werner.

When they are finished, Werner asks: "How long did we actually play?"

Petra answers: "I don't know, but I looked out the window and counted that the tram passed by our house exactly ten times in that time, heading towards the city. The first tram came when we started the game, and the tenth one came when we just finished."

(The tram runs every 20 minutes.)

How long did Petra and Werner play?
Between the first passing tram and the tenth tram, there are $9 \cdot 20=180$ minutes, as the trams run at 20-minute intervals.

Petra and Werner thus played for 180 minutes $=3$ hours.