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If a fair coin is tossed 7 times, what is the probability, to the nearest thousandth, of getting exactly 5 tails?
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If a fair coin is tossed 77 times, what is the probability, to the nearest thousandth, of getting exactly 55 tails?\newlineAnswer:

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Q. If a fair coin is tossed 77 times, what is the probability, to the nearest thousandth, of getting exactly 55 tails?\newlineAnswer:
  1. Identify Problem Type: Identify the type of probability problem.\newlineWe are dealing with a binomial probability problem because we have a fixed number of independent trials (77 coin tosses), two possible outcomes (heads or tails), and we want to find the probability of getting exactly 55 tails.
  2. Binomial Probability Formula: Determine the binomial probability formula.\newlineThe binomial probability formula is P(X=k)=(nk)(pk)((1p)(nk))P(X = k) = \binom{n}{k} \cdot (p^k) \cdot ((1-p)^{(n-k)}), where:\newline- P(X=k)P(X = k) is the probability of getting kk successes in nn trials,\newline- (nk)\binom{n}{k} is the binomial coefficient,\newline- pp is the probability of success on a single trial, and\newline- (1p)(1-p) is the probability of failure on a single trial.
  3. Calculate Binomial Coefficient: Calculate the binomial coefficient (nk)n \choose k. For our problem, n=7n = 7 (number of trials) and k=5k = 5 (number of successes, i.e., tails). (75)7 \choose 5 = 7!5!(75)!\frac{7!}{5! \cdot (7-5)!} = 7!5!2!\frac{7!}{5! \cdot 2!} = 7621\frac{7 \cdot 6}{2 \cdot 1} = 422\frac{42}{2} = 2121.
  4. Determine Success and Failure: Determine the probability of success pp and failure 1p1-p. Since the coin is fair, the probability of getting tails (success) on a single trial is p=0.5p = 0.5, and the probability of getting heads (failure) is also 0.50.5.
  5. Calculate Probability of 55 Tails: Calculate the probability of getting exactly 55 tails.\newlineUsing the binomial probability formula:\newlineP(X=5)=(75)(0.55)(0.575)P(X = 5) = \binom{7}{5} \cdot (0.5^5) \cdot (0.5^{7-5})\newlineP(X=5)=21(0.55)(0.52)P(X = 5) = 21 \cdot (0.5^5) \cdot (0.5^2)\newlineP(X=5)=210.031250.25P(X = 5) = 21 \cdot 0.03125 \cdot 0.25\newlineP(X=5)=210.0078125P(X = 5) = 21 \cdot 0.0078125\newlineP(X=5)=0.1640625P(X = 5) = 0.1640625
  6. Round Probability: Round the probability to the nearest thousandth. P(X=5)P(X = 5) rounded to the nearest thousandth is approximately 0.1640.164.

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