The grades on the last history exam had a mean of 80%. Assume the population of grades on history exams is known to be normally distributed with a standard deviation of 5. What percent of students earn a score between 70% and 80%?

Question

anonymous · Answer

0.022

 0.477

 0.50

 0.522

amistre64 · Answer

the difference from 70 to 80 is 10

and since 80 is the mean .... how many standard deviations go into 10?  then use the empirical rule unless a higher degree of accuracy is needed

anonymous · Answer

What is the empirical rule?
@amistre64

anonymous · Answer

And there are two standard deviations into 10.  Correct?

amistre64 · Answer

correct

so, by the empirical rule,  there is .95 of the data in the interval from -2 to 2

we only want the interval from -2 to 0,  so half of it.... what is half of .95?

anonymous · Answer

0.475.  So then what?

amistre64 · Answer

the then what should be obvious .. pick an option

anonymous · Answer

but that's not one of my options.  There is 0.477.  Is it that one?

amistre64 · Answer

thats the most 'obvious' one yes :)

anonymous · Answer

Thank you

amistre64 · Answer

good luck