Mental Maths Strategies

Being able to calculate quickly in your head is a huge advantage on the CSSE maths paper. The exam is timed, and many questions can be solved faster using mental strategies than by writing out full column methods. This lesson teaches you the most useful techniques.

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Why Mental Maths Matters for the CSSE

The CSSE maths paper covers both arithmetic and problem-solving in a single paper. There are many questions to answer in a limited time. If you can do simple calculations mentally, you will have more time for the trickier multi-step questions. Think of mental maths as your speed tool.

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Strategy 1: Partitioning

Break numbers into parts that are easier to work with.

Worked Example

Calculate 47 + 36 mentally.

• 47 + 30 = 77
• 77 + 6 = 83

Answer: 83

Worked Example

Calculate 156 - 38 mentally.

• 156 - 30 = 126
• 126 - 8 = 118

Answer: 118

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Strategy 2: Compensating (Rounding and Adjusting)

Round one number to the nearest 10 or 100, do the calculation, then adjust.

Worked Example

Calculate 67 + 29 mentally.