April 2000
MA214 : DISCRETE MATHEMATICS

QUESTION 4

Total Marks: 15 Marks

• Question 1
• Question 2
• Question 3
• Question 5
• Cover Page

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SUGGESTED SOLUTIONS
for Question 4

(a)Use De Morgan ’s laws to write negations for the following statements.
(i)Chee Leong is a multimedia major and Chee Leong ’s sister is a computer science major.[2 marks ]
(ii)The power is switched off or the machine is unplugged.[2 marks ]

(b)Construct truth tables for the following statements.

Which statement is a tautology and which is a contradiction?Justify your
answer.[2 marks ]

(c)Disprove the following statements by giving a counterexample.
(i)The product of any two prime numbers is prime.[1 mark ]
(ii)The difference of any two odd integers is odd.[1 mark ]
(iii)For all integers is a prime number.[1 mark ]