Exercise 2: The Complement Rule Applied to an Error Rate — Possible Solution
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GIVEN
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500 total requests, 15 of which returned an error.

STEP 1: THE PROBABILITY OF AN ERROR
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P(error) = 15 / 500 = 0.03 (3%)

STEP 2: APPLYING THE COMPLEMENT RULE
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"Did not return an error" is exactly the complement of "returned an
error." Per this chapter's own complement rule:

  P(not error) = 1 - P(error) = 1 - 0.03 = 0.97

So there's a 97% probability that a randomly selected request from
that week did not return an error.

STEP 3: CONFIRMING BY DIRECT COUNT
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500 - 15 = 485 requests did not error.
485 / 500 = 0.97, matching the complement-rule result exactly.

WHY THIS WORKS AS AN ANSWER
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The complement rule is applied directly using this chapter's own
formula rather than separately counting non-error requests from
scratch, and the result is then independently confirmed by a direct
count, showing both approaches agree.