Alright, I've tried to calculate this with empirical rule formula and it's not correct. then I've tried with Chebyshev's theorem and it's wrong. what the hell. how to solve this? thank you for your explanation and help.
A government agency reported that the mean retail price per gallon of regular grade gasoline was $3.47. Suppose that the standard deviation was $0.20 and that the retail price per gallon has a bell-shaped distribution.
a) What percentage of regular grade gasoline sold between $3.27 and $3.67 per gallon?
b) What percentage of regular grade gasoline sold between $3.27 and $3.87 per gallon?
c) What percentage of regular grade gasoline sold for more than $3.87 per gallon?
a) b) c) Convert to z space via z = (x-avg)/std. Then use a z table to find the requested area between the range.
Or, a) you are at +- 1 std. Use the 68-95-99.7 rule. U can even use it for b) & c). But perhaps the precision (sig digits) are not enough. Which is why you may need to ue the more precise values from the z table.
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