Each successful attempt will increment the swords damage by 1, and each unsuccessful attempt will decrement it by 1. The sword's damage will not decrease beyond it's default damage.

- I'm able to enchant the sword a maximum of 4 times.

- Each enchantment level has a specific pass/fail chance rate.

- Level 1 Enchantment - 80%

- Level 2 Enchantment - 50%

- Level 3 Enchantment - 20%

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I'm able to to calculate these independent events:

Chance of success from Level 0 to 1 = 80%

Chance of success from Level 0 to 2 = 4/5 * 1/2 = 40%

Chance of success from Level 0 to 3 = 4/10 * 2/10 = 8%

Chance of success from Level 0 to 4 = 2/25 * 2/25 = 0.64%

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Since you can fail a level, without going back to level 0. How would I go about adding the fail rates to the calculated succession rates?