If scores are normally distributed with a mean of 50 and a standard deviation of 10

If scores are normally distributed with a mean of 50 and a standard deviation of 10, what percent of the scores is:
(a) below 50?
(b) between 30 and 55?
(c) greater than 70?

Solution Summary

Normal distribution and standard deviation is determined.

The IQ scoresarenormallydistributedwith a mean of 100 and a standard deviation of 15.
1. What is the probability that a random person has an IQ between 85 and 115?
2. Find the 90th percentile of the IQ distribution.
3. If a random sample of 100 people is selected, what is the standard deviation of the sample mean?

1. What are the characteristics of the normal curve? What human behavior, trait, or characteristic can you think of that is distributednormally?
2. Standard scores, such as z scores, allow us to make comparisons across different samples. Why?
3. Why is a z score a standard score, and why can standard scores be used to com

Probability, Sampling Distributions, and Inference
1) If light bulbs have lives that arenormallydistributedwith a mean of 2500 hours and a standard deviation of 500 hours, what percentage of light bulbs have a life less than 2500 hours?
2) The lifetimes of light bulbs of a particular type arenormallydistributedwith

Suppose that scores on a particular test arenormallydistributedwith a mean of 120 and a standard deviation of 19. What is the minimum score needed to be in the top 5% of the scores on the test? Carry your intermediate computations to at least four decimal places, and round your answer to at least one decimal place.

Assume that a set of test scores is normallydistributedwith a mean of 100 and a standard deviation of 20. Use the 68-95-99.7 rule to find the following quantities:
Suggestion: make a drawing and label first
a. Percentage of scores less than 100
b. Relative frequency of scores less than 120
c. Percentage of scores less

A cutoff score of 79 has been established for a sample of scores in which the mean is 65. If the corresponding z-score is 1.4 and the scoresarenormallydistributed, what is the standard deviation?

1.) Test one: mean is 80 and standard deviation is 9. Mark scores 91
Test two: mean is 77 and standard deviation is 6. Mark score 87
Find the percentile for all
Which test Mark did better? Why?
2.) What is the the standard deviation for IQ tests? If someone's IQ is 140, how many standard deviation is it above the

The scores on a lab test arenormallydistributedwithmean of 200. If the standard deviation is 20, find
a) The score that is 2 standard deviations below the mean
b) The percentage of scores that fall between 180 and 240
c) The percentage of scores above 240
d) The percentage of scores between 200 and 260
e) The percentag

The scores of males on the 2008 Mathematical Scholastic Aptitude Test (MSAT) were approximately normallydistributedwithmean µ = 500 and standard deviation σ = 100 points (approximately). Find the proportion of males who received the following scores.
a. Between 500 and 600
b. Between 400 and 600