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Class 6 Computer Science — What is an algorithm?

Follow an algorithm step by step to find what it produces, and explain why changing the order of the steps changes the answer.

Name: ________________________

  1. 1.Some steps just do something. Others ask a question first and go one way or the other. Sort each step.

    Groups: Just does something · Asks a question first

    • If the box is empty, fill it
    • Add 5 to the total
    • Show the answer on the screen
    • If the answer is right, say well done
    • If the total is over 20, stop
    • Double the number

  2. 2.Which of these describes an algorithm best?

    • a) Another name for the keyboard
    • b) A picture of what a program will look like
    • c) A machine that runs inside the computer
    • d) A list of clear steps, in order, that finishes the job

  3. 3.Another algorithm says: start with 4, then add 3, then double it. What number do you end with?

  4. 4.Put these steps in the order a computer runs them to add two numbers and show the total.

    • Show the total on the screen
    • Read the two numbers
    • Add the two numbers together

  5. 5.An algorithm says: start with 12, then halve it, then halve it. What number do you end with?

  6. 6.Match each short algorithm to the number it ends with.

    • Start with 3, then double it
    • Start with 3, then add 4
    • Start with 10, then halve it
    • Start with 4, then double it
    • Start with 4, then multiply it by 3
    • 8
    • 7
    • 5
    • 6
    • 12

  7. 7.Why must every algorithm come to an end?

    • a) Because the screen would run out of room
    • b) Because every algorithm must have exactly five steps
    • c) Because computers can only hold ten steps at a time
    • d) Because a set of steps that never finishes never gives an answer

  8. 8.An algorithm says: start with 20, then halve it, then take away 3. What number do you end with?

Answer key — Class 6 Computer Science — What is an algorithm?

  1. 1. Add 5 to the total → Just does something; If the total is over 20, stop → Asks a question first; Show the answer on the screen → Just does something; If the box is empty, fill it → Asks a question first; Double the number → Just does something; If the answer is right, say well done → Asks a question first
  2. 2. d) A list of clear steps, in order, that finishes the job
  3. 3. 14
  4. 4. 1. Read the two numbers 2. Add the two numbers together 3. Show the total on the screen
  5. 5. 3
  6. 6. Start with 3, then double it → 6; Start with 3, then add 4 → 7; Start with 10, then halve it → 5; Start with 4, then double it → 8; Start with 4, then multiply it by 3 → 12
  7. 7. d) Because a set of steps that never finishes never gives an answer
  8. 8. 7