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A distribution of measurements is relatively mound-shaped with a mean of 80 and a standard deviation of 11.
Use this information to find the proportion of measurements in the given interval.
less than 91
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They want to say that the measurements are normally distributed, but do not use
this term trying to perplex you.
Notice that 91 = 80 + 11; in other words, the upper bound of 91 is one standard deviation
above the mean value.
The empirical rule says that 68% of data are within one standard deviation.
As a reference, use this link
https://www.investopedia.com/terms/e/empirical-rule.asp#:~:text=The%20Empirical%20Rule%20states%20that,standard%20deviations%20from%20the%20mean.
or any textbook on statistics.
For you, it means that half, or 0.5 of all measurements are below 80 and 0.34 = of
all measurements are between 80 and 0.91.
In all, 0.5 + 0.34 = 0.84 of all measurements are less than 91.
At this point, the problem is just solved.
ANSWER. The proportion of measurements below 91 is 0.84.
Solved.