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Grade 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.Those two algorithms use the same starting number and the same two steps, but end differently. Why?

    • a) Because the steps were done in a different order
    • b) Because one of the two must be wrong
    • c) Because 4 is an even number
    • d) Because doubling is not allowed twice

  2. 2.An algorithm says: start with 2, then multiply it by 5, then add 1. What number do you end with?

  3. 3.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

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

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

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

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

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

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

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

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

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

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

  1. 1. a) Because the steps were done in a different order
  2. 2. 11
  3. 3. 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
  4. 4. c) Because a set of steps that never finishes never gives an answer
  5. 5. 1. Read the two numbers 2. Add the two numbers together 3. Show the total on the screen
  6. 6. d) A list of clear steps, in order, that finishes the job
  7. 7. 7
  8. 8. 3