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Cost equation for daily pass:
C_daily = 67x + 25x = 92x, where x = # days skied
Cost equation for season pass:
C_season = 350 + 25x
We wish to find x such that C_season < C_daily
350 + 25x < 92x
350 < 67x
350/67 < x
5.224 < x
x = 6 ski days
Sanity check...
#days skied Daily pass cost Season pass cost
4 368 450
5 460 475
6 552 500 <---- Season pass becomes cheaper
If you plot the two cost equations, the point where they cross is the point where the season pass becomes more cost effective (well, the nearest integer above where they cross).
The green line represents the season pass cost equation:
