– I had a strange dream last night.
– Tell me all about it.
– I went to see car racing.
– I didn’t know you cared for cars.
– Before the race the cars were parked in a square fashion.
– What do you mean?
– There were equally many cars each column and row.
– You mean that there were a square numbers of cars?
– I guess you could put it like that.
– Then what?
– After the race they were parked in a rectangular shape with 5 more in each row than in the square lineup.
– How many were there in each column?
– You tell me!
The Royal Spanish Mathematics Society is 100 years old this year. The newspaper El País celebrates this with a math problem every week. The problem above is, in essence, one of them. Here is a video presenting the problem (in Spanish).