Description
Question 1 (15 pts)
2019 novel coronavirus (2019-nCoV) is a newly emerged coronavirus
with global implications. The attached zip file contains csv files that
report the number of cumulative cases reported around the world
from Jan 21- Feb 14 (source JHU CSSE
https://github.com/CSSEGISandData/COVID-19).
Please choose one data visualization scheme to show what you find
in these data and explain why you choose this kind of visualization.
Question 2 (15 pts)
A researcher studies text messages and sleep in teenagers. Consider
the following data for text messages sent per day and average hours
of sleep for five teenagers.
Texts per day Hours of sleep
132 4.2
52 8
77 6
115 5.2
209 3.2
(a) Find the sample mean and standard deviation of texts per day
and hours of sleep.
(b) Find the correlation coefficient r between texts per day and hours
of sleep. Describe what your value of r means.
Question 3 (10 pts)
Consider three relations Student, Course and CourseEnrollment, with
the schema defined below.
• The Student relation stores students’ information,
including StudentID, StudentName and Department;
• The Course relation stores courses’ information,
including CourseID, CourseName and Credit;
• The CourseEnrollment relation stores the information of
students taking courses and the grades, and a student may take
multiple courses.
Student Relation
StudentID StudentName Department
11111 Jane Smith Math
11112 Mike Green Music
… … …
Course Relation
CourseID CourseName Credits
1001 Calculus 3
1002 Physics 3
… … …
CourseEnrollment Relation
StudentID CourseID Grade
11111 1001 A
11111 1002 B
11112 1001 A-
… … …
(a) Write a SQL statement for the query: find the names of students
from “Math” department and also take the “1001” course;
(b) Write a relational algebra expression for the query: find the
names of students who have taken course “Calculus”;
Bonus (10 point)
Please explain why there is n-1 instead of n in sample standard
deviation
� = #∑ (�’ − �̅) , +
‘
� − 1
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End.
