Chicago Cubs First-Place Elimination Scenario
Chicago must win 21 more games (50 total) to avoid elimination from first place.
Here are the final standings in a scenario in which Chicago finishes in first place with 50 wins:

Team             W	L	PCT	GB
Chicago          50	112	0.309	0.00
Cincinnati       50	112	0.309	0.00
Milwaukee        49	113	0.302	1.00
St. Louis        48	114	0.296	2.00
Pittsburgh       47	115	0.290	3.00

Tie breakers
Chicago wins the series with Cincinnati 8 games to 5

To construct the scenario, we start with the current standings in the division:
Team             W	L	GL	PCT	GB
Milwaukee        32	20	110	0.615	0.0
St. Louis        29	24	109	0.547	3.5
Cincinnati       29	25	108	0.537	4.0
Chicago          29	26	107	0.527	4.5
Pittsburgh       29	26	107	0.527	4.5

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

Chicago currently has 4 win(s) against Cincinnati and 0 loss(es).
Chicago wins 4 additional game(s) against Cincinnati and loses 5.
Chicago wins the series 8 games to 5.
Chicago wins 0 additional game(s) against teams outside the division and loses 67.

Chicago currently has 0 win(s) against Milwaukee and 3 loss(es).
Chicago wins 10 additional game(s) against Milwaukee and loses 0.
Chicago wins the series 10 games to 3.
Chicago wins 0 additional game(s) against teams outside the division and loses 67.

Chicago currently has 1 win(s) against Pittsburgh and 4 loss(es).
Chicago wins 0 additional game(s) against Pittsburgh and loses 8.
Chicago loses the series 1 games to 12.
Chicago wins 0 additional game(s) against teams outside the division and loses 67.

Chicago currently has 0 win(s) against St. Louis and 0 loss(es).
Chicago wins 7 additional game(s) against St. Louis and loses 6.
Chicago wins the series 7 games to 6.
Chicago wins 0 additional game(s) against teams outside the division and loses 67.

Cincinnati currently has 0 win(s) against Milwaukee and 0 loss(es).
Cincinnati wins 2 additional game(s) against Milwaukee and loses 11.
Cincinnati loses the series 2 games to 11.
Cincinnati wins 0 additional game(s) against teams outside the division and loses 68.

Cincinnati currently has 1 win(s) against Pittsburgh and 5 loss(es).
Cincinnati wins 7 additional game(s) against Pittsburgh and loses 0.
Cincinnati wins the series 8 games to 5.
Cincinnati wins 0 additional game(s) against teams outside the division and loses 68.

Cincinnati currently has 1 win(s) against St. Louis and 1 loss(es).
Cincinnati wins 7 additional game(s) against St. Louis and loses 4.
Cincinnati wins the series 8 games to 5.
Cincinnati wins 0 additional game(s) against teams outside the division and loses 68.

Milwaukee currently has 1 win(s) against Pittsburgh and 2 loss(es).
Milwaukee wins 6 additional game(s) against Pittsburgh and loses 4.
Milwaukee wins the series 7 games to 6.
Milwaukee wins 0 additional game(s) against teams outside the division and loses 68.

Milwaukee currently has 3 win(s) against St. Louis and 1 loss(es).
Milwaukee wins 0 additional game(s) against St. Louis and loses 9.
Milwaukee loses the series 3 games to 10.
Milwaukee wins 0 additional game(s) against teams outside the division and loses 68.

Pittsburgh currently has 2 win(s) against St. Louis and 5 loss(es).
Pittsburgh wins 6 additional game(s) against St. Louis and loses 0.
Pittsburgh wins the series 8 games to 5.
Pittsburgh wins 0 additional game(s) against teams outside the division and loses 76.

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