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statistics, normal distribution, mean,standard deviation?
Your local pizza chain claims that the delivery time of their pizzas is normally distributed with a mean of 30 minutes and a standard deviation of 10 minutes.
A. You order a single pizza and it takes 42 minutes to arrive at your house. Do you have reason to disbelieve the chain’s claim?
B. Later, twenty of your friends in different random locations order pizzas. The average delivery time is 42 minutes. Now do you have reason to disbelieve the chain’s claim?
2 Answers
- BeeFreeLv 79 years agoFavorite Answer
John
A - No reason to disbelieve the claim since 42 minutes is only 1.2 standard deviations greater than the expected value of 30
B. With a sample of 20, using a t-test, the p-value equals 0.000035 which is REALLY REALLY small. It is unlikely the mean is 30 minutes.
Hope that helped
- ?Lv 69 years ago
A. You are only 1.2 standard deviations away from the average, so for 1 reading, it is possible that the claim is still valid. There is really no reason to disbelieve at this point.
B. When over time, many of the readings are out of the standard deviation, it is less likely that the claim is valid. But at this point, more information is needed to decide on the claim. If the times were all clustered around 42 minutes, there is good reason to disbelieve the claim. But if most of them are clustered around 30, and there was 1 or 2 readings WAY outside of the average, you might end up with an average of 42 ( 19 of the deliveries were at 30 minutes and 1 at 270 minutes would give an average of 42 minutes). In this second case, the oddball datum would allow you to still believe the claim.
