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The probability of winning a game is 
1//1000. If you play this game 500 times, what is the probability that you win at least twice?

The probability of winning a game is 1/1000 1 / 1000 . If you play this game 500500 times, what is the probability that you win at least twice?

Full solution

Q. The probability of winning a game is 1/1000 1 / 1000 . If you play this game 500500 times, what is the probability that you win at least twice?
  1. Identify probability of not winning: Identify the probability of not winning the game.\newlineThe probability of not winning the game is the complement of the probability of winning the game.\newlineProbability of not winning = 1Probability of winning=111000=99910001 - \text{Probability of winning} = 1 - \frac{1}{1000} = \frac{999}{1000}.
  2. Calculate probability of winning once: Calculate the probability of winning exactly once in 500500 tries.\newlineThis can be done using the binomial probability formula:\newlineP(X=k)=C(n,k)(pk)((1p)(nk))P(X = k) = C(n, k) \cdot (p^k) \cdot ((1-p)^{(n-k)})\newlineWhere:\newlineP(X=k)P(X = k) is the probability of kk successes in nn trials,\newlineC(n,k)C(n, k) is the number of combinations of nn things taken kk at a time,\newlinepp is the probability of success on a single trial, and\newlinenn is the number of trials.\newlineFor winning exactly once:\newlineP(X=k)=C(n,k)(pk)((1p)(nk))P(X = k) = C(n, k) \cdot (p^k) \cdot ((1-p)^{(n-k)})00\newlineP(X=k)=C(n,k)(pk)((1p)(nk))P(X = k) = C(n, k) \cdot (p^k) \cdot ((1-p)^{(n-k)})11
  3. Calculate probability of never winning: Calculate the probability of never winning in 500500 tries.\newlineThis is simply the probability of not winning raised to the power of the number of tries:\newlineP(X=0)=(9991000)500P(X = 0) = (\frac{999}{1000})^{500}
  4. Calculate probability of winning at least twice: Calculate the probability of winning at least twice. The probability of winning at least twice is the complement of the probability of winning fewer than two times (which includes winning exactly once and never winning). P(X \geq 2) = 1 - P(X < 2) P(X < 2) = P(X = 0) + P(X = 1) P(X2)=1(P(X=0)+P(X=1))P(X \geq 2) = 1 - (P(X = 0) + P(X = 1))
  5. Perform calculations: Perform the calculations using the results from Steps 22 and 33.\newlineP(X2)=1((999/1000)500+500×(1/1000)×(999/1000)499)P(X \geq 2) = 1 - ((999/1000)^{500} + 500 \times (1/1000) \times (999/1000)^{499})
  6. Simplify expression: Simplify the expression. This step involves arithmetic calculations to simplify the expression obtained in Step 55.

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