[Rob Russo]

This is probably common knowledge, but this chart quickly shows the total number of laps in a 20-minute race.

Find your lap time between two of the numbers and use the lap count of the faster time above it.

laps   time (to nearest tenth second)

23      0:52.2
22      0:54.6  
21      0:57.1  
20      1:00  
19      1:03.2  
18      1:06.7  
17      1:10.6  
16      1:15  
15      1:20  
14      1:25.7  
13      1:32.3  
12      1:40  
11      1:49.1  
10      2:00  
9        2:13.3  
8        2:30  
7        2:51.4  
6        3:20  
5        4:00 
4        5:00

In the interests of having to think less, drive more...