Mark schemes
Q1.
All marks AO2 (apply)
Marking guidance for examiners
•   Award marks for working out until an incorrect step has been made.
•   If, in any one step, a candidate is simplifying different parts of an expression simultaneously award all relevant marks for this multiple stage but don’t award any further marks for working in any parts simplified incorrectly. For example, if the expression P.P.(P+Q) + P.P.1 was changed to P.(P+Q)+P.0, the candidate would get one mark for simplifying the first part to P.(P+Q) and could get further marks for correctly simplifying this part of the expression further but should not be awarded marks for simplifying the incorrectly changed part P.0 (ie to 0)
1 mark for final answer: A + B
Max 3 for working. Award up to two marks for applying each one of the three techniques (one mark per application):
•   a successful application of De Morgan’s Law (and any associated cancellation of NOTs) that produces a simpler expression.
•   applying an identity other than cancelling NOTs that produces a simpler expression.
•   successfully expanding brackets.
Note: A simpler expression is one that is logically equivalent to the original expression but uses fewer logical operators.
Max 3 if correct final answer but any incorrect working
Example Solution (1)

Example Solution (2)

Example Solution (3)

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Q2.
(a)  All marks AO2 (apply)
 
Input	 	Outputs	
A	B	C	D	E	F	G	H	
0	0	0	0	0	0	0	0	
0	0	1	1	0	0	0	1	
0	1	1	0	1	0	1	0	
1	1	1	0	1	0	1	1	
1 mark: Column D correct or column E or column F correct
1 mark: Column G correct
1 mark: Column H correct
Max 2 if any incorrect values in table
3
(b)  All marks AO2 (apply)
B⋅C+A⋅(B⨁C)
1 mark: B⋅C or B⨁C somewhere in expression
1 mark: A is ANDed with B⨁C
1 mark: Fully correct expression
A. award second mark even if brackets around B⊕C are missing
A. use of AND, OR, XOR instead of symbols
A. (B̅⋅C)+(B⋅C̅) for (B⨁C)
If a student has written an expression but then tried to simplify it and made an error then mark the original expression that the student has written down and ignore the simplification.
3
(c)  Mark is for AO2 (analyse)
It adds together its inputs // it is a full adder circuit;
N.E. half-adder, adder
1
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