The number of marshmallows an adult can fit in their mouth is skewed right with a mean of 6.5 and a standard deviation of 0.58. What is the probability that a random sample of 40 adults would have a mean of at least 7 marshmallows?

For a sample of 40 adults, the sampling distribution of the sample mean is approximately normal by the Central Limit Theorem. Its standard error is 0.58/√40 ≈ 0.0917, so 7 is (7 − 6.5)/0.0917 ≈ 5.45 standard errors above the mean. The probability of a sample mean at least 5.45 standard errors above the mean is essentially 0, so the correct choice is A, approximately 0.

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