Four Operations

The four operations — addition, subtraction, multiplication, and division — are the building blocks of arithmetic. On the CSSE maths paper, you will need to carry out calculations quickly and accurately, often as part of multi-step word problems. This lesson covers the key methods you need.

---

Addition

Column Addition

Write numbers one below the other, lining up the ones, tens, hundreds, and so on. Always start from the right (the ones column).

Worked Example

Calculate 4,657 + 2,385

	Th	H	T	O
	4	6	5	7
+	2	3	8	5
=	7	0	4	2

• Ones: 7 + 5 = 12. Write 2, carry 1.
• Tens: 5 + 8 + 1 = 14. Write 4, carry 1.
• Hundreds: 6 + 3 + 1 = 10. Write 0, carry 1.
• Thousands: 4 + 2 + 1 = 7.

Answer: 7,042

---

Subtraction

Column Subtraction (Decomposition)

When a digit on the top is smaller than the digit below, you must exchange (borrow) from the next column to the left.

Worked Example

Calculate 6,304 - 2,857

• Ones: 4 - 7 — cannot do it. Borrow from the tens. But tens digit is 0, so borrow from hundreds (3 becomes 2, tens becomes 10, then tens becomes 9 and ones becomes 14). 14 - 7 = 7.
• Tens: 9 - 5 = 4.
• Hundreds: 2 - 8 — cannot do it. Borrow from thousands. 12 - 8 = 4.
• Thousands: 5 - 2 = 3.

Answer: 3,447

Exam Tip: Always check your subtraction by adding your answer to the smaller number. 3,447 + 2,857 = 6,304. Correct!

---

Multiplication

Short Multiplication (by a single digit)

Worked Example

Calculate 463 × 7

• 3 × 7 = 21. Write 1, carry 2.
• 6 × 7 = 42, plus 2 = 44. Write 4, carry 4.
• 4 × 7 = 28, plus 4 = 32.

Answer: 3,241

Long Multiplication (by a two-digit number)

Worked Example

Calculate 256 × 34

Step 1: Multiply 256 × 4 = 1,024

Step 2: Multiply 256 × 30 = 7,680

Step 3: Add the partial products: 1,024 + 7,680 = 8,704