【Question 11】  
Wang Wei walks from place A to place B, while at the same time, Zhang Ming rides a bicycle from place B to place A. Half an hour later, the two meet on the way. After Zhang Ming arrives at place A, he immediately returns to place B, and 20 minutes after the first meeting, he catches up with Wang Wei again. After Zhang Ming reaches place B, he turns back again, and the two meet for the third time $\qquad$ minutes after the second meeting.
【Analysis and Solution】
From departure to the first face-to-face meeting, the two people together walked 1 full distance, taking 30 minutes; from departure to the second face-to-face meeting (the third meeting), the two people together walked 3 full distances, taking $30 \times 3=90$ minutes; the two people met for the third time after $90-30-20=40$ minutes following the second meeting.