This is THE DISAPPEARING BICYCLIST puzzle by 18th Century mathematician Sam Loyd. In position 'A' 13 boys are visible, but in position 'B' - only 12. One is invited to determine which boy has disappeared and where did he go.

This is THE DISAPPEARING BICYCLIST puzzle by 18th Century mathematician Sam Loyd. In position 'A' 13 boys are visible, but in position 'B' - only 12. One is invited to determine which boy has disappeared and where did he go.