OCR Computer Science for A Level
Teaching and Learning Resources
Chapter 14: Logic gates and Boolean algebra
ANSWERS TO QUESTIONS IN THE STUDENT’S BOOK
Page 176
Question
1. Simplify the expression (A∧¬A)∨B.
Answer
B
Question
2. Simplify the expression (A∨B)∨(A∧C).
Answer
AvB
Question
3. Simplify the expression ¬(A∧¬B)∨(¬A∧B).
Answer
¬A v B
Question
4. Simplify the expression (A∧B)∨(¬A∧B).
Answer
B
Question
5. Simplify the expression (A∧B)∨(A∧(B∧C))∨(B∧(B∨C)).
Answer
B
Page 181
Question
Using Karnaugh maps, simplify the following expressions:
1. A∧B∨A∧¬B
2. A∧B∧C∨A∧¬B∧C∨A∧B∧¬C
3. ¬A∧¬B∧¬C∨¬A∧B∨A∧B∧¬C∨A ∧C
4. ¬A∧B∧C∧D∨¬A∧B∧C∧¬D∨A∧B ∧C∧D∨A∧B∧C∧¬D
OCR Computer Science for A Level Chapter 14
© Hodder & Stoughton Limited 2015
OCR Computer Science for A Level
Teaching and Learning Resources
Answer
1. A
2. (A∧B) v (A∧C)
3. (A∧C)v(¬A v ¬C) v B
4. C∧B
Page 182
Question
1. Simplify the expression: ¬A∧B∧¬C∧¬Dv¬A∧B∧¬C∧DvA∧B ∧¬C∧¬DvA∧B ∧¬C∧D.
Answer
B∧¬C
Question
2. Draw a diagram showing how two half adders can be combined to form a full adder.
Answer
Question
3. Draw a diagram showing how an 8-bit adder can be made from a series of full adders.
Answer
Question
4. State the purpose of inputs to and outputs from a D-type flip-flop and draw a circuit for a Dtype flip-flop using NAND gates.
OCR Computer Science for A Level Chapter 14
© Hodder & Stoughton Limited 2015
OCR Computer Science for A Level
Teaching and Learning Resources
Answer
There are two inputs: a control and a clock; the flip-flop can only change values when
triggered by the clock signal. The value of the flip-flop is held or delayed until the next
clock signal. There are two outputs; one is the negative of the other.
OCR Computer Science for A Level Chapter 14
© Hodder & Stoughton Limited 2015