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Posted by **Betty** on Sunday, August 12, 2012 at 8:35pm.

Q-3a: What is the probability that the mean time spent per customer is at least 3 minutes?

- Statistic -
**MathMate**, Sunday, August 12, 2012 at 9:39pmIt is not mentioned that the distribution is normal. We will assume that it is, either by assumption, or by an approximation using the central limit theorem (which preferably applies to samples of 30+).

With the assumption, we can see that the variance is σ²/n=0.4²/16=0.01, hence σ=0.1.

Look up the Normal distribution table for 1-tail probability of 1σ which gives the probability of 1-0.8413=0.1587 for*less*than μ-1σ=3.1-0.1=3.0 minutes.

Can you take it from here?

- Statistic -
**ronnie**, Thursday, October 24, 2013 at 11:37pmNo

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