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1CP2-CT-1.1 Problems, algorithms, sequence and IPO

Part 1 of 7 · 1CP2-CT-1 · Programming foundations

The opening Computational thinking worksheet, establishing what an algorithm is before any Python is written.

Students will:

  • tell an algorithm apart from a restatement of the problem
  • say what makes a set of steps followable by someone else
  • put steps into a sequence that can actually be carried out
  • label the input, processing and output stages of a task
  • write and then improve a short informal algorithm

Inside: 9 explanation cells, 2 multiple-choice questions, 4 fill-in-the-blanks cells and 2 written answers. 20 marks, about 45 minutes.

Series: 1CP2-CT-1 · Programming foundations, part 1 of 7.

Shared by Coding PathwayVerified teacher

  • 17 cells
  • About 45 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026

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The whole resource, exactly as a class sees it. Answers and marking are held back.

Problems, algorithms, sequence and IPO

Computational thinking begins before code. It starts with understanding a problem and describing a solution precisely enough to follow.

In this worksheet you will learn how to:

  • distinguish a problem, an algorithm and a program;
  • recognise a finite, ordered and unambiguous algorithm;
  • explain why sequence matters;
  • identify input, processing and output;
  • write and improve short informal algorithms.

There is no Python in this worksheet. The ideas are established first so that code in Worksheet 3 has a clear meaning.

1. From a problem to a result

Problem to resultProblemAlgorithmProgramResultThe algorithm is the ordered solution method. A program is one executable implementation.

A problem is a goal or task that needs a solution. An algorithm is a finite, ordered sequence of unambiguous steps that solves the problem or completes the task. A program is one implementation written in a programming language so a computer can execute it.

The algorithm is not tied to one language. The same solution method could be implemented in different programs.

Multiple choice1 mark

Which option is an algorithm for finding the number of seats in 6 rows of 8?

  • AThe goal of finding the total number of seats.
  • BA completed application that displays a seating plan.
  • CReceive 6 and 8, multiply them, then output the total.
  • DSome unordered ideas about rows and seats.

2. What makes an algorithm followable?

Every useful algorithm has four qualities:

QualityMeaningWeak exampleImproved example
FiniteIt reaches an end.Keep checking forever.Check each of the five boxes, then stop.
OrderedSteps appear in the order required.Output the total before calculating it.Calculate the total, then output it.
UnambiguousEach step has one clear meaning.Deal with the numbers.Add the two supplied numbers.
PurposefulThe steps complete the stated task.Display an unrelated message.Display the calculated total.

A short algorithm can still be incomplete. The test is whether another person could follow it without guessing missing data, operations or order.

Fill in the blanks3 marks
A followable algorithm must reach an end, so it is label 1. Its steps happen in a stated sequence, so it is label 2. Each step has one clear meaning, so it is label 3.
  • ambiguous
  • finite
  • ordered
  • programmed
  • unambiguous

3. Sequence

A sequence performs instructions one after another in their stated order.

Consider an algorithm for making a name card:

  1. Receive the person's name.
  2. Join Welcome, to the name.
  3. Output the completed message.

Step 2 cannot produce the complete message before the name is available. Step 3 cannot output the completed message before it has been created. Sequence therefore affects what data exists at each point and whether the task can succeed.

Fill in the blanks4 marks
Complete the sensible order for a ticket-total algorithm. 1. label 1 2. label 2 3. label 3 4. label 4
  • Calculate the total price.
  • Output the total price.
  • Receive the number of tickets.
  • Receive the price of one ticket.
  • Output a total before any values are known.

4. Input, processing and output

Input, processing and outputInputdata suppliedProcessingwork on the dataOutputinformation producedSequence matters: data must be available before it is processed, and processed before it is reported.

Input is data supplied to the algorithm. It does not only mean something typed at a keyboard. Processing is the work carried out using that data. Output is the information produced.

For 6 rows with 8 seats per row:

  • input: 6 rows and 8 seats per row;
  • processing: multiply 6 by 8;
  • output: a total of 48 seats.
Fill in the blanks3 marks
In a parcel-weight algorithm, the number of parcels and weight of one parcel are the label 1. Multiplying them is the label 2. The total weight is the label 3.
  • input
  • output
  • problem
  • processing
  • program

5. Writing an informal algorithm

An informal algorithm uses precise ordinary language rather than programming syntax.

Requirement: A storeroom has 5 shelves with 7 boxes on each shelf. Find and report the total number of boxes.

Complete model:

  1. Receive the number of shelves, 5, and boxes per shelf, 7.
  2. Multiply 5 by 7 to calculate the total number of boxes.
  3. Output the total number of boxes, 35.

Each mark-worthy idea is visible: the required data, the operation and the produced result. Vague phrases such as “get the information” or “work it out” would make the method ambiguous.

Written answer3 marks

Write a three-step informal algorithm for this task: a library has 9 boxes with 4 books in each box. Calculate and report the total number of books.

Number the steps. State the supplied values, the operation and the output in executable order.

Students type their answer here.

6. Improving an algorithm

A useful review checks three things:

  1. Completeness: are all required inputs, operations and outputs present?
  2. Precision: can every step be followed without guessing?
  3. Order: is each value available before it is used?

Weak method: Get some numbers. Find the answer. Show it.

Improved method: Receive the number of packs and items per pack. Multiply them to calculate the total. Output the total number of items.

The improved method names the data, processing and output while remaining independent of a programming language.

Multiple choice1 mark

Why is “Calculate the total, then receive the two values” not a valid sequence for this task?

  • AAlgorithms are not allowed to contain calculations.
  • BThe calculation tries to use values before they are available.
  • CEvery algorithm must begin with an output.
  • DThe two values must always be equal.

7. Apply the model in a new context

A school orders 7 trays with 6 plants in each tray. A good solution must preserve this chain:

supplied values → multiplication → reported total

When explaining why the order matters, name the dependency: processing needs both input values, and the output needs the processed result.

Written answer2 marks

Explain why the three stages in the plant-order algorithm must remain in the order input, processing, output. Apply your answer to the supplied values 7 and 6.

Build a short chain: what becomes available, what uses it, and what can then be reported.

Students type their answer here.

Fill in the blanks3 marks
A label 1 states the goal. An label 2 gives an ordered solution method. A label 3 is an executable implementation.
  • algorithm
  • output
  • problem
  • processing
  • program

Ready for the next step

You can now distinguish a problem, algorithm and program, judge whether steps are finite and precise, follow sequence and identify IPO.

Next, you will use decomposition and abstraction to make larger problems easier to understand before any code is introduced.