10 REM Monty Hall problem
20 LET N = 10000
30 RANDOMIZE
40 LET W = 0
50 FOR G = 1 TO N
60 LET S = 0
70 GOSUB 230
80 IF V = 0 THEN 100
90 LET W = W+1
100 NEXT G
110 PRINT "NOT switching doors wins car in";
120 PRINT W/N*100; "per cent of games."
130 LET W = 0
140 FOR G = 1 TO N
150 LET S = 1
160 GOSUB 230
170 IF V = 0 THEN 190
180 LET W = W+1
190 NEXT G
200 PRINT "But switching doors wins car in";
210 PRINT W/N*100; "per cent of games."
220 END
230 REM ** Is game won?
240 REM Play one game.
250 REM Switching if and only if S <> 0.
260 REM Randomly place car behind a door.
270 LET C = INT(RND*3)
280 REM Player randomly chooses a door.
290 LET P0 = INT(RND*3)
300 REM Monty opens door revealing a goat.
310 LET M = INT(RND*3)
320 IF M = C THEN 310
330 IF M = P0 THEN 310
340 IF S = 0 THEN 410
350 REM Player switches to remaining door.
360 LET P = INT(RND*3)
370 IF P = P0 THEN 360
380 IF P = M THEN 360
390 GOTO 430
400 REM Player sticks with original door.
410 LET P = P0
420 REM Victory?
430 IF P <> C THEN 460
440 LET V = 1
450 RETURN
460 LET V = 0
470 RETURN