Chicago Cubs First-Place Eliminiation Scenario
Chicago must win 22 more games (41 total) to avoid elimination from first place.
Here are the final standings in a scenario in which Chicago finishes in first place with 41 wins:

Team             W	L	PCT	GB
Chicago          41	121	0.253	0.00
Pittsburgh       41	121	0.253	0.00
Cincinnati       40	122	0.247	1.00
Milwaukee        40	122	0.247	1.00
St. Louis        40	122	0.247	1.00

Tie breakers
Chicago wins the series with Pittsburgh 7 games to 6

To construct the scenario, we start with the current standings in the division:
Team             W	L	GL	PCT	GB
Milwaukee        19	11	132	0.633	0.0
Chicago          19	12	131	0.613	0.5
Cincinnati       16	15	131	0.516	3.5
St. Louis        14	17	131	0.452	5.5
Pittsburgh       14	18	130	0.438	6.0

Next, we show how the remaining series of games plays out in the scenario:

Chicago currently has 0 win(s) against Cincinnati and 0 loss(es).
Chicago wins 13 additional game(s) against Cincinnati and loses 0.
Chicago wins the series 13 games to 0.
Chicago wins 0 additional game(s) against teams outside the division and loses 79.

Chicago currently has 0 win(s) against Milwaukee and 0 loss(es).
Chicago wins 2 additional game(s) against Milwaukee and loses 11.
Chicago loses the series 2 games to 11.
Chicago wins 0 additional game(s) against teams outside the division and loses 79.

Chicago currently has 0 win(s) against Pittsburgh and 0 loss(es).
Chicago wins 7 additional game(s) against Pittsburgh and loses 6.
Chicago wins the series 7 games to 6.
Chicago wins 0 additional game(s) against teams outside the division and loses 79.

Chicago currently has 0 win(s) against St. Louis and 0 loss(es).
Chicago wins 0 additional game(s) against St. Louis and loses 13.
Chicago loses the series 0 games to 13.
Chicago wins 0 additional game(s) against teams outside the division and loses 79.

Cincinnati currently has 1 win(s) against Milwaukee and 2 loss(es).
Cincinnati wins 10 additional game(s) against Milwaukee and loses 0.
Cincinnati wins the series 11 games to 2.
Cincinnati wins 0 additional game(s) against teams outside the division and loses 82.

Cincinnati currently has 0 win(s) against Pittsburgh and 0 loss(es).
Cincinnati wins 1 additional game(s) against Pittsburgh and loses 12.
Cincinnati loses the series 1 games to 12.
Cincinnati wins 0 additional game(s) against teams outside the division and loses 82.

Cincinnati currently has 0 win(s) against St. Louis and 0 loss(es).
Cincinnati wins 13 additional game(s) against St. Louis and loses 0.
Cincinnati wins the series 13 games to 0.
Cincinnati wins 0 additional game(s) against teams outside the division and loses 82.

Milwaukee currently has 2 win(s) against Pittsburgh and 2 loss(es).
Milwaukee wins 1 additional game(s) against Pittsburgh and loses 8.
Milwaukee loses the series 3 games to 10.
Milwaukee wins 0 additional game(s) against teams outside the division and loses 90.

Milwaukee currently has 3 win(s) against St. Louis and 0 loss(es).
Milwaukee wins 9 additional game(s) against St. Louis and loses 1.
Milwaukee wins the series 12 games to 1.
Milwaukee wins 0 additional game(s) against teams outside the division and loses 90.

Pittsburgh currently has 0 win(s) against St. Louis and 0 loss(es).
Pittsburgh wins 1 additional game(s) against St. Louis and loses 12.
Pittsburgh loses the series 1 games to 12.
Pittsburgh wins 0 additional game(s) against teams outside the division and loses 82.

# Chicago Cubs' magic number
# Chicago's magic number
# Cubs' magic number
# MLB Playoff Race