Question

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%?

0.022

0.477

0.50

0.522

Answer 1

@ganeshie8

Answer 2

80 - 70 = 10. The standard deviation is 5. Therefore the grade of 70% is 2 standard deviations below the mean. The empirical rule states that for all normal distributions approximately 95% of the data points lie within the range of plus and minus 2 standard deviations of the mean. In this case only half of the data points in this range are needed, so the required percentage is half of 95%.

Answer 3

so i would divide that by 1/2

Answer 4

Sir/Ma'am, A Warm Welcome To Open Study.
Sir/Ma'am please show your Working for the question you have posted.

Answer 5

A survey of 1,000 men and women asked, "Do you earn over $50,000 per year?" The table below shows the responses for males and females:


Male Female Total
Income over $50,000 485 385 870
Income below $50,000 65 65 130
Total 550 450 1,000


Based on these data, are "being male" and "earning over $50,000" independent events?
Yes, P(being male | the person earns over $50,000) ≠ P(being male)

Yes, P(being male | the person earns over $50,000) = P(being male)

No, P(being male | the person earns over $50,000) ≠ P(being male)

No, P(being male | the person earns over $50,000) = P(being male) @ganeshie8

Answer 6

Independent events: P(A and B) = P(A)P(B)

P(male, >50k) = 485/1000 = .485
P(male) = 550/1000 = .550
P(>50k) = 870/1000 = .870

P(male)P(>50k) = .4785 not 0.485 thus not independent

The options seem to use another criterion, however.

Answer 7

Ok

Answer 8

I guess if independent then
P(being male and >50k/yr) = P(being male)
because making >5ok would not make you more or less likely to be a male.

Answer 9

u should give me a medal ;P

Answer 10

i think its C