Twelve Flags

Twelve flags stand equidistant along the track at the stadium. The runners start at the first flag. A runner reaches the eighth flag 8 seconds after he starts. If he runs at an even speed, how many seconds does he need altogether to reach the twelfth flag?


He will need 1247 seconds, not 12 seconds.

There are 7 segments from the first flag to the eighth, and 11 from the first to the twelfth. He runs each segment in 87 seconds; therefore, 11 segments take 887 = 1247 seconds.