Truth Tables — Edexcel GCSE CS

Warm-up · Gates 1 of 2

AND & OR Gates

Complete the output column for each basic logic gate below. Remember: AND outputs 1 only when both inputs are 1. OR outputs 1 when at least one input is 1.

[4 marks]

Score: 0 / 8

Table 1 — AND Gate

Output = A AND B

A	B	A AND B
0	0
0	1
1	0
1	1

AND truth: 0,0→0 · 0,1→0 · 1,0→0 · 1,1→1

Table 2 — OR Gate

Output = A OR B

A	B	A OR B
0	0
0	1
1	0
1	1

OR truth: 0,0→0 · 0,1→1 · 1,0→1 · 1,1→1

Warm-up · Gates 2 of 2

NOT Gate & Combined NOT + AND

Complete the output columns below. NOT flips a single input (0→1, 1→0). The second table combines NOT and AND — first apply NOT to A, then AND the result with B.

[4 marks]

Score: 0 / 6

Table 3 — NOT Gate

Output = NOT A (single input)

A	NOT A
0
1

NOT truth: 0→1 · 1→0

Table 4 — Combined: (NOT A) AND B

Step 1: NOT A → Step 2: (NOT A) AND B

A	B	NOT A
0	0	1
0	1	1
1	0	0
1	1	0

Result: 0,0→0 · 0,1→1 · 1,0→0 · 1,1→0

Activity 1 · Computational Thinking

Two-Variable Logic — AND, OR, NOT

The table below uses two inputs A and B. The logical expression for Q is already given. Complete the truth table by writing the logical expressions for S and T, then fill in all missing values.

[5 marks]

Score: 0 / 5

Part (i) — Write the logical expressions

Hint: look at when S = 1 in the table

Hint: look at when T = 1 in the table

Part (ii) — Complete the Q column

A	B	S	T	Q
Inputs		?	?	NOT S AND T

🔌 Logic Reference

AND1 only if BOTH inputs = 1

OR1 if AT LEAST ONE input = 1

NOTFlips the value (0→1, 1→0)

NANDNOT AND — opposite of AND

NORNOT OR — opposite of OR

XOR1 if inputs are DIFFERENT

A	B	AND	OR	XOR
0	0	0	0	0
0	1	0	1	1
1	0	0	1	1
1	1	1	1	0

Activity 2 · Computational Thinking

Three-Variable Logic — Exam Style

Here is a partially completed truth table. The logical expression for Q is complete. Complete the truth table to give the logical expression for S and T, and the values for Q.

[3 marks]

Score: 0 / 10

Write logical expressions for S and T

When is S = 1? Look at rows 7 and 8 (A=1, C=1)

When is T = 0? Only when B=0 AND C=0

Complete the Q column

A	B	C	S	T	Q
Inputs			?	?	NOT S AND T

🔌 Logic Reference

AND1 only if BOTH inputs = 1

OR1 if AT LEAST ONE = 1

NOTFlips the value

NOT S AND T means:

→ First compute S

→ Then NOT S

→ Then AND with T

Q = (NOT S) AND T

Example: row where A=1,B=0,C=1

S = A AND C = 1 AND 1 = 1

T = B OR C = 0 OR 1 = 1

NOT S = NOT 1 = 0

Q = 0 AND 1 = 0

Activity 3 · Computational Thinking

Two Variables — NOT and OR Combined

The logical expression for Q is already given. Deduce the expressions for S and T from the values shown, then complete the Q column.

[5 marks]

Score: 0 / 6

Part (i) — Write the logical expressions

Hint: S = 1 when A = 0, and S = 0 when A = 1

Hint: T = 0 only when both A = 0 and B = 0

Part (ii) — Complete the Q column

A	B	S	T	Q
Inputs		?	?	S AND T
0	0	1	0
0	1	1	1
1	0	0	1
1	1	0	1

🔌 Reminder

S AND T = 1 only when

both S = 1 AND T = 1

Step through each row:

1. Find S from A

2. Find T from A, B

3. Q = S AND T

Activity 4 · Computational Thinking

Three Variables — Exam Style

Here is a partially completed truth table. The logical expression for Q is complete. Complete the truth table to give the logical expressions for S and T, and all values for Q.

[3 marks]

Score: 0 / 10

Write logical expressions for S and T

Hint: S = 0 only when A = 0 AND B = 0

Hint: T flips with every change in C

Complete the Q column

A	B	C	S	T	Q
Inputs			?	?	S AND T
0	0	0	0	1
0	0	1	0	0
0	1	0	1	1
0	1	1	1	0
1	0	0	1	1
1	0	1	1	0
1	1	0	1	1
1	1	1	1	0

🔌 Reminder

Q = S AND T

→ Q = 1 only when

S = 1 AND T = 1

Worked example row 3:

A=0, B=1, C=0

S = 0 OR 1 = 1

T = NOT 0 = 1

Q = 1 AND 1 = 1