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Empirical rule

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The lifespans of gorillas in a particular zoo are normally distributed. The average gorilla lives 20, point, 8 years; the standard deviation is 3, point, 1 years.
Use the empirical rule left parenthesis, 68, minus, 95, minus, 99, point, 7, percent, right parenthesis to estimate the probability of a gorilla living less than 23, point, 9 years.
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text