Decomposition: breaking down problems

Splitting big problems into smaller subproblems that are easier to solve

Name:

Date:

Try each question. If you're stuck, leave it and come back. The answer key is on the last page.

1
What does 'decomposition' mean in computing? A) Breaking a big problem into smaller parts B) Deleting files from a computer C) Joining lots of small problems together D) Letting food rot
Answer:
2
True or false? Decomposition makes problems harder to solve. A) True B) False
Answer:
3
Put these subproblems in order for making a sandwich. Put these in order: Get the bread, Spread butter on the bread, Add the filling, Cut the sandwich
Answer:
4
What is decomposition in computing? A) Breaking a big problem into smaller parts B) Adding numbers together C) Drawing a picture D) Saving a file
Answer:
5
You want to write a program for a quiz. Which of these is the best way to decompose the problem? A) Ask the question, get the answer, check the answer, give a score B) Write the whole program in one big block C) Wait for someone else to do it D) Buy a quiz app from a shop
Answer:
6
Match each big problem to a good first subproblem. Match each item on the left to one on the right. Left: Make a game, Build a website, Plan a school trip, Bake a cake Right: Decide the rules, Plan the pages, List the people going, Collect the ingredients
Answer:
7
Why is decomposition useful when working with a team? A) Different people can solve different subproblems at the same time B) Only one person has to do everything C) It stops the team from talking D) It makes the program smaller in size
Answer:
8
True or false? Every subproblem from decomposition can itself be decomposed further. A) True B) False
Answer:
9
You are coding a maze game. Which of these is NOT a useful subproblem to think about? A) What colour socks the player is wearing B) How the player moves C) How the walls are drawn D) How to detect when the player wins
Answer:
10
Decompose 'write a story program' into subproblems in a sensible order. Put these in order: Plan the characters and setting, Write the opening line, Build the rest of the story step by step, Print the finished story to the screen
Answer:

Answer key

Decomposition: breaking down problems · for parents and teachers

1
Breaking a big problem into smaller parts
Decomposition is splitting a big, hard problem into smaller, easier subproblems. Each part can then be solved on its own.
2
False
Decomposition actually makes problems easier. Smaller pieces are simpler to think about and code.
3
Get the bread, Spread butter on the bread, Add the filling, Cut the sandwich
Making a sandwich decomposes into four smaller steps. Each step is a subproblem you can do one at a time.
4
Breaking a big problem into smaller parts
Decomposition means breaking a big problem into smaller, easier parts.
5
Ask the question, get the answer, check the answer, give a score
A quiz program decomposes neatly into: ask question, take input, check answer, update score. Each part can be coded separately.
6
Make a game → Decide the rules; Build a website → Plan the pages; Plan a school trip → List the people going; Bake a cake → Collect the ingredients
Decomposition starts with sensible first steps. You cannot bake without ingredients or run a trip without knowing who is coming.
7
Different people can solve different subproblems at the same time
Once a problem is decomposed, team members can each take a subproblem. This makes work faster and lets people focus.
8
True
Yes. You can keep decomposing. 'Make icing' breaks into 'measure sugar', 'add butter', 'mix' and so on. You stop when the steps are simple enough.
9
What colour socks the player is wearing
Good decomposition focuses on the parts that affect the program. Sock colour does not affect the maze, so it is not a useful subproblem.
10
Plan the characters and setting, Write the opening line, Build the rest of the story step by step, Print the finished story to the screen
Each subproblem follows logically. Planning first, then opening, then body, then output is a sensible order.