Question 7 (1 point)

Consider a decision tree constructed for a classification problem, where the possible classes are A, B and C. How many branches does an arbitrary internal node in the decision tree have?

Question 7 options:

	1
	2
	3
	4
	it varies, depending on what attribute the node branches on

Question 8 (1 point)

info([a, b]) =

Question 8 options:

	entropy(-a, -b)
	entropy(a, b)
	entropy(a/(a+b), b/(a+b))
	entropy(-a/(a+b), -b/(a+b))
	-(a/(a+b))entropy(a/(a+b)) - (b/(a+b))entropy(b/(a+b))

Question 9 (1 point)

Consider the process of constructing a decision tree based on the training set in Table 1 and using the information gain algorithm discussed in class. What is the information gain when branching at the root of the decision tree on the attribute Aquatic?

Table 1: Vertebrate Dataset (modified from Introduction to Data Mining by Tan et al.)

Name	Body temp	Give birth	Aquatic	Class
human	warm	yes	no	mammal
echidna	warm	no	no	mammal
salmon	cold	no	yes	fish
whale	warm	yes	yes	mammal
eel	cold	no	yes	fish
bat	warm	yes	no	mammal
shark	cold	yes	yes	fish
cat	warm	yes	no	mammal

Question 9 options:

	(1/2)info([4,0]) + (1/2)info([1,3])
	info([5,3]) (1/2)info([4,0]) (1/2)info([1,3])
	(5/8)info([1,4]) + (3/8)info([3,0])
	info([5,3]) (5/8)info([1,4]) (3/8)info([3,0])
	none of the above

Question 10 (1 point)

If we are going to build a decision tree for the dataset in Table 1, which attribute (not considering Name) will be selected as the root?

Table 1: Vertebrate Dataset (modified from Introduction to Data Mining by Tan et al.)

Name	Body temp	Give birth	Aquatic	Class
human	warm	yes	no	mammal
echidna	warm	no	no	mammal
salmon	cold	no	yes	fish
whale	warm	yes	yes	mammal
eel	cold	no	yes	fish
bat	warm	yes	no	mammal
shark	cold	yes	yes	fish
cat	warm	yes	no	mammal

Question 10 options:

	Body temp
	Give birth
	Aquatic
	one of Give birth or Aquatic, since it is a tie, randomly pick one
	any of the three attributes

Question 11 (1 point)

When the decision tree built from the previous question is used on the test instance in Table 2, what is the predicted class for porcupine?

Table 2: Test Instance

Name	Body temp	Give birth	Aquatic	Class
porcupine	warm	yes	no	?

Question 11 options:

	mammal
	fish
	cannot decide