Common Core: S-CP.7
Problem 21 of 25sta-021
Twenty cards are numbered 1 through 20, and one card is drawn at random. What is the probability that its number is even or a multiple of 5?
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Solution walkthrough1:37
- Lay out all cards. "Even or a multiple of " wins if at least one of the two is true.
- Even numbers: . That is cards.
- Multiples of : . That is cards, but and are already counted.
- Count each card once: cards, so the probability is .
- Traps: counts and twice, counts only even cards, only cards in both.