April 1999
MA214: DISCRETE MATHEMATICS

QUESTION 5

Total Marks: 20 Marks

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SAMPLE STUDENT'S SOLUTIONS
for Question 5

 

(a) (i) How many functions are there from a set with three elements to a set with four elements? Explain your answer. [2]
(ii) How many functions are there from a set with four elements to a set with three elements? Explain your answer.

 

[2]
(b) (i) How many one-to-one functions are there from a set with three elements to a set with four elements? Explain your answer. [2]
(ii) How many one-to-one functions are there from a set with four elements to a set with three elements? Explain your answer.

 

[2]
(c) (i) How many onto functions are there from a set with three elements to a set with four elements? Explain your answer. [2]
(ii) How many onto functions are there from a set with four elements to a set with three elements? Explain your answer.

 

[2]
(d) (i) How many invertible functions are there from a set with three elements to a set with four elements? [1]
(ii) How many invertible functions are there from a set with four elements to a set with three elements?

 

[1]
(e) Construct a function from three elements to two elements which is neither one-to-one nor onto.

 

[2]
(f) The relation R, "is a factor of " is defined on pic7.gif (99 bytes). Decide whether or not R is reflexive, symmetric or transitive. [4]