A survey of 1000 us gas stations found that the price charged for a gallon of regular gas can be closely approximated by a normal distribution with a mean of 1.90 and a standard deviation of .20.
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This is two standard deviations above and below the mean. If I remember my statistics, this means that 95% of the stations charge within this standard deviation range.
So, 950 out of 1000
So, 950 out of 1000
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Notice that 1.50 and 2.30 are both 0.4 away from the mean (1.90).
0.4 is twice the standard deviation.
Therefore 1.50 is two standard deviations below the mean, and 2.30 is two standard deviations above the mean.
Checking a book or a website like the one below, you should find that for a normal distribution, 95% of the data is within two standard deviations of the mean.
and so 95% of the 1000 gas stations charge between 1.50 and 2.30 :)
0.4 is twice the standard deviation.
Therefore 1.50 is two standard deviations below the mean, and 2.30 is two standard deviations above the mean.
Checking a book or a website like the one below, you should find that for a normal distribution, 95% of the data is within two standard deviations of the mean.
and so 95% of the 1000 gas stations charge between 1.50 and 2.30 :)
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my result is 95.45%