Brooklyn College, CUNYPSYCHOLOGY 3400 1

Brooklyn College, CUNYPSYCHOLOGY 3400

1.The results from a statistics class' first exam are as follows: The average grade obtained on the exam by its 25 students is an 83, with a standard deviation of 11 points. Answer the following based on this information:

a. Approximately how many people received a failing grade (less than 65)?

b. What percentage of people received a grade between a 70 and a 91?

c. What percentage of individuals received a score whose z-score was -.70 or less?

d. What grade is required in order to be in the top 15 percent? The top 10 percent?

e. What percentage of people received a grade between 85 and 95?

f. What percentage of people received a grade of 94 or less?

g. What grade is required to be in the bottom 20%?  

h. What z-score is required to be in the top 40%?

i. What percentage of individuals have a z-score between -1 and 1.40?

j. What percentage of individuals have a z-score between 1.05 and 1.40?

2. An ethologist is interested in how long it takes a certain species of water shrew to catch its prey. He only has access to a sample of 100 shrews. On multiple occasions each day he lets a dragonfly loose inside the cage of the shrews and times how long it takes until the shrews catch the dragonfly. After months of research the ethologist concludes 1) that the mean prey catching time was 30 seconds, 2) the standard deviation was 5.5 seconds and 3) that the scores he has collected are normally distributed. What is the percentage of shrews that:

a) catch a dragonfly in less than 18 seconds;

b) catch a dragonfly in between 22 and 45 seconds;

c) take longer than 45 seconds to catch a dragonfly?

d) take less than 30 seconds to catch its prey;