SOLUTION: Some teachers grade �on a (bell) curve� based on the belief that classroom test scores are normally distributed. One way of doing this is to assign a �C� to all scores within one s

Question 944220: Some teachers grade �on a (bell) curve� based on the belief that classroom test scores are normally distributed. One way of doing this is to assign a �C� to all scores within one standard deviation of the mean. Then, the teacher would assign a �B� to all scores between one and two standard deviations above the mean, an �A� to all scores more than two standard deviations above the mean, and use symmetry to define the regions for �D� and �F� on the left side of the normal curve.
If 200 students take an exam, the number of students who would
receive a �B� is_____.
Answer by Theo(13342) (Show Source): You can put this solution on YOUR website!
you can use the rule of thumb for normal distribution to figure this out.
the rule is:

68% are within 1 standard deviation from the mean.
95% are within 2 standard deviations from the mean.

the difference between 95 and 68 are the percent that are between 1 and 2 standard deviations from the mean plus or minus.

the difference between 100% and 95% are the percent that are greater than 2 standard deviations from the mean plus or minus.

you will get:

68% are within 1 standard deviation from the mean.

95% - 68% = 27% are between 1 standard deviation and 2 standard deviations from the mean.

100% - 95% = 5% are beyond 2 standard deviations from the mean.

Since A and B are above the mean and D and F are below the mean, and since the distribution curve is symmetric, you will get:

68% will get a C because they are within 1 standard from the mean. Half of them will be above the mean and half of them will be below the mean.

13.5% will get a B because they are between 1 and 2 standard deviations above the mean.

13.5% will get a D because they are between 1 and 2 standard deviations below the mean.

2.5% will get an A because they are beyond 2 standard deviations above the mean.

2.5% will get an F because they are beyond 2 standard deviations below the mean.

Add up all the percentages and you get 68 + 2 * 13.5 + 2 * 2.5 = 100%.

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