LNF Cymru Literacy and numeracy for Wales

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GCSE Computer Science

Numeracy is heavy and specific: learners convert between denary, binary and hexadecimal, add in binary, work with base 2 storage units, calculate image, sound and compressed file sizes and routing costs, and reason with truth tables and DIV and MOD. Literacy centres on close reading of the Unit 2 scenario and requirements, precise technical vocabulary, short and extended judgement answers in Unit 1, and code annotation and test commentaries. The single biggest thing Key Stage 3 should build is fluent place value in base 2 and base 16, so that storage and file size calculations become routine.

Awarding body
WJEC
Level
Level 1 and Level 2
First taught
September 2025
Amount of literacy work
Medium
Amount of numeracy work
High
Specification
Open the specification
How this qualification is assessed
  • Unit 1: Understanding Computer Science: Digital examination 1 hour 30 minutes, 50%, 80 marks
  • Unit 2: Computer Programming: On-screen examination based on a pre-released brief, 2 hours, 50%, 80 marks, set and marked by WJEC

Skills that use Calculation

  1. Converting between denary, binary and hexadecimal

    Assessed: In the exam

    Learners convert between denary, binary and hexadecimal, perform binary addition, use arithmetic shifts and explain overflow and underflow. All of this rests on secure place value and powers of 2.

    Numeracy: The number system, Calculation, Relationships within the number system, Conceptual understanding, Fluency, Logical reasoning

    Getting pupils ready

    Year 7
    Pupils use binary place-value cards from 128 down to 1 to make their age and house number, write each as 8-bit binary and check by adding the place values.
    Year 8
    Pupils add two 8-bit binary numbers in columns, convert the answer to denary to check it, and explain in one sentence what happens when a ninth bit is needed.
    Year 9
    Pupils convert web colour codes such as FF8800 from hexadecimal to denary and binary, and show that a left shift of one place doubles a binary number.
    Show the specification wording and the LNF statements

    Where it is in the specification: Unit 1, Section 1.2.1, page 13

    “convert between, denary, binary and hexadecimal counting systems”
    Progression step 3

    • I can read and write numbers to 1 million and numbers to 3 decimal places.

    • I can add and subtract numbers using whole numbers and decimals.

    • I can use a range of strategies to check calculations including the use of inverse operations, equivalent calculations and the rules of divisibility.

    Progression step 4

    • I can use powers and understand the importance of powers of 10.

    • I can represent a concept in different ways, flowing between different representations including verbal, concrete, visual, digital and abstract.

    • I can use the four operations and the connections between them, e.g. apply division as the inverse of multiplication.

    Progression step 5

    • I can represent a concept in different ways, flowing between different representations including verbal, concrete, visual, digital and abstract.

    • I can use firmly established, memorable and usable facts and techniques in order to apply the most efficient methods.

    • I can verify and prove results and solutions.

  2. Data storage units and capacity

    Assessed: In the exam

    Learners must know the base 2 storage units from bit and nibble to petabyte, where each step is 1,024 not 1,000, and calculate the capacity needed to store data.

    Numeracy: Measurement, Calculation, The number system, Relationships within the number system, Communicating with symbols, Fluency, Conceptual understanding

    Getting pupils ready

    Year 7
    Pupils order bit, nibble, byte, kilobyte, megabyte and gigabyte on a class washing line and work out how many bits are in one kilobyte.
    Year 8
    Pupils work out how many 3 MB photos fit on a 16 GB memory stick, first estimating with 1,000 and then calculating with 1,024, and explain the difference.
    Year 9
    Pupils total the file sizes in a sample project folder, convert the total into the most sensible unit and judge whether it fits their school network storage allowance.
    Show the specification wording and the LNF statements

    Where it is in the specification: Unit 1, Section 1.2.1, pages 13 to 14

    “the relationship between data storage units using the base 2 prefixes”
    Progression step 3

    • I can convert metric units of length to smaller units, e.g. cm to mm, m to cm, km to m.

    • I can multiply numbers and decimals by a multiple of 10, e.g. 15 x 30, 1.4cm x 20.

    • I can read and write numbers to 1 million and numbers to 3 decimal places.

    Progression step 4

    • I can use the common units of measure, convert between related units of the metric system and carry out calculations.

    • I can use powers and understand the importance of powers of 10.

    • I can read and write numbers of any size.

    Progression step 5

    • I can use appropriate notation, symbols and units of measurement, including compound measures.

    • I can use firmly established, memorable and usable facts and techniques in order to apply the most efficient methods.

    • I can interpret answers within the context of the problem and consider whether answers, including calculator, analogue and digital displays, are sensible.

  3. Calculating file sizes for images and sound

    Assessed: In the exam

    Learners calculate the storage needed for graphics from dimensions and colour depth, and for sound from sampling rate, bit depth and length, then convert the result into suitable units.

    Numeracy: Shape and space, Calculation, Strategic competence, Measurement, Communicating with symbols

    Getting pupils ready

    Year 7
    Pupils draw an 8 by 8 pixel icon on squared paper using four colours, find the number of pixels as an area and work out that each pixel needs 2 bits.
    Year 8
    Pupils use width times height times colour depth to calculate the file size of their pixel art in bits and bytes, then predict what doubling the colour depth does.
    Year 9
    Pupils record a 10 second sound clip in Audacity, calculate its size from sample rate, bit depth and length, and compare their answer with the saved file size.
    Show the specification wording and the LNF statements

    Where it is in the specification: Unit 1, Section 1.2.1, page 13

    “how to calculate the storage requirements for graphics using different dimensions, bit depths and colour depths.”
    Progression step 3

    • I can find areas by counting squares, progressing to calculating the area of squares and rectangles using formulae.

    • I can multiply 2- and 3-digit numbers by a 2-digit number.

    • I can prioritise and organise the relevant steps needed to complete the task or reach a solution.

    Progression step 4

    • I can demonstrate an understanding of the relationship between a formula representing a measurement and the units used.

    • I can use the order of operations including brackets and powers.

    • I can prioritise and organise the relevant steps needed to complete the task or reach a solution.

    Progression step 5

    • I can recognise, model and apply the underlying mathematical structures and ideas within problems, in order to formulate and solve them.

    • I can refine methods of recording calculations.

    • I can understand and use a variety of compound measures.

  4. Compression ratios and file size reduction

    Assessed: In the exam

    Learners calculate compression ratios and the reduction in file size after lossy or lossless compression, and judge whether the saving is worth the loss of quality.

    Numeracy: Calculation, Relationships within the number system, Conceptual understanding, Logical reasoning

    Getting pupils ready

    Year 7
    Pupils run-length encode rows of their pixel art, for example 5 white then 3 black, and count how many characters they save compared with listing every pixel.
    Year 8
    Pupils zip a folder of text files, record the size before and after, and write the saving as a ratio in its simplest form.
    Year 9
    Pupils save one photo as PNG and at three JPEG quality settings, calculate the percentage reduction for each and explain which methods are lossy.
    Show the specification wording and the LNF statements

    Where it is in the specification: Unit 1, Section 1.2.1, page 14

    “calculation of compression ratios and the reduction in file sizes following compression.”
    Progression step 3

    • I can use ratio and proportion to calculate quantities.

    • I can calculate a percentage, fraction and decimal of any quantity with a calculator where appropriate.

    • I can use equivalence of fractions, decimals and percentages to compare proportions.

    Progression step 4

    • I can express one quantity as a percentage of another.

    • I can calculate a percentage increase or decrease.

    • I can use equivalence of fractions, decimals and percentages to select the most appropriate one for a calculation.

    Progression step 5

    • I can use multipliers as an efficient method when working with percentages, e.g. multiply by 1.2 to increase an amount by 20%.

    • I can interpret answers within the context of the problem and consider whether answers, including calculator, analogue and digital displays, are sensible.

    • I can explain results and procedures precisely using appropriate mathematical language.

  5. Logical operators, truth tables and computing operators

    Assessed: In the exam

    Learners use AND, OR, NOT and XOR in truth tables to solve problems, and apply the relational operators and integer division (DIV and MOD) set out in Appendix B when tracing and writing algorithms.

    Numeracy: Logical reasoning, Communicating with symbols, Calculation

    Getting pupils ready

    Year 7
    Pupils complete AND and OR truth tables for a burglar alarm that sounds only when it is switched on and a door is open, then test it with switch cards.
    Year 8
    Pupils use DIV and MOD to turn a number of seconds into minutes and seconds for a Scratch quiz timer, checking three answers by hand.
    Year 9
    Pupils write conditions using >=, <= and <> for a cinema ticket price program and complete a truth table showing which ages each condition accepts.
    Show the specification wording and the LNF statements

    Where it is in the specification: Unit 1, Section 1.6.1, page 19; Appendix B, pages 34 to 35

    “the use of logical operators in truth tables to solve problems”
    Progression step 3

    • I can justify my procedures and predictions.

    • I can use appropriate notation, symbols and units of measurement.

    • I can use mental strategies to recall multiplication tables up to 10 x 10 and use to solve division problems.

    Progression step 4

    • I can justify my procedures, predictions and conjectures.

    • I can use appropriate notation, symbols and units of measurement, including compound measures.

    • I can use the four operations and the connections between them, e.g. apply division as the inverse of multiplication.

    Progression step 5

    • I can construct and develop a mathematical argument.

    • I can use appropriate notation, symbols and units of measurement, including compound measures.

    • I can explain results and procedures precisely using appropriate mathematical language.

  6. Calculating the cost of routing data

    Assessed: In the exam

    Learners calculate the cost of routing data across a network by adding link costs along possible routes and comparing the totals to find the cheapest.

    Numeracy: Strategic competence, Calculation, Fluency

    Getting pupils ready

    Year 7
    Pupils find the cheapest route for a message between rooms on a school map where each corridor has a cost, adding the totals for three routes.
    Year 8
    Pupils list every route between two routers on a six-node network diagram with decimal link costs, add each total and circle the lowest.
    Year 9
    Pupils recalculate the cheapest route when one link on a network diagram fails and write a sentence justifying their new choice with the totals.
    Show the specification wording and the LNF statements

    Where it is in the specification: Unit 1, Section 1.3.1, page 15

    “cost calculation of routing data on a network.”
    Progression step 3

    • I can select, trial and evaluate a variety of possible approaches and break problems into a series of tasks.

    • I can add and subtract numbers using whole numbers and decimals.

    • I can select and apply appropriate checking strategies.

    Progression step 4

    • I can select, trial and evaluate a variety of possible approaches and break complex problems into a series of tasks.

    • I can use efficient written methods to add and subtract numbers and decimals of any size, including a mixture of large and small numbers with differing numbers of decimal places.

    • I can select and apply appropriate checking strategies.

    Progression step 5

    • I can select, trial and evaluate a variety of possible approaches and break complex problems into a series of tasks.

    • I can prioritise and organise the relevant steps needed to complete the task or reach a solution.

    • I can select and apply appropriate checking strategies.

Good to know

Links with other qualifications

Place value, powers, ratio and percentage reduction are taught in Mathematics, so agreeing shared language (for example 'column value' and 'simplest form') with the Mathematics department in Years 7 to 9 will help pupils transfer these skills to binary and file size work.

Source: WJEC GCSE Computer Science specification, teaching from 2025, for award from 2027, Version 3, September 2025.