An Agreed Code: How the Same Bits Mean Letters or Colours · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Both ends must use the same code

Computing · Computing Fundamentals · ages 12-13
Name ______________________   Date ____________

  1. Two friends want secret notes. What must they share first?

    • The same pen
    • The same code
    • The same birthday

  2. What does a bit pattern mean all by itself?

    • Nothing, until a code gives it meaning
    • Always a letter
    • Always a number

  3. The same bit pattern can stand for two different things in two different files.

    Circle one:   True   False

  4. You send Ij, but your friend decodes with a two-step shift and reads Hk. What happened?

    • The two ends used different codes
    • The letters were too short
    • The paper was the wrong colour

  5. You shift each letter one step forward, so Hi becomes Ij. Your friend shifts one step back to read it. Why does she succeed?

    • She uses a nicer pen
    • She reverses the same agreed rule
    • She guesses every word

  6. Name two things the same eight bits could stand for in two different files.

    • A letter in one file and a shade of grey in another
    • A letter in both, always the same letter
    • Nothing in either file

  7. Computer A sends bits meaning Hi. Computer B prints 18537. A friend blames a broken cable. What is the sharper answer?

    • Hi and 18537 are the same message
    • The cable is guilty, buy a new one
    • The cable is fine, the ends used different codes

  8. A pager shows 143, and teens read it as I love you. Why does that code work for them?

    • The numbers force every phone to play music
    • Both sides know that 1, 4, and 3 count the letters in each word
    • The number 143 is magic
LightMySky · lightmysky.comW1-mt_IQY-PHtZVZ-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Both ends must use the same code W1-mt_IQY-PHtZVZ-s1

  1. The same code · Matching codes let the writer encode and the reader decode.
  2. Nothing, until a code gives it meaning · Bits borrow meaning from the code both ends agree to use.
  3. True · Each file reads bits with its own code, like letter versus shade of grey.
  4. The two ends used different codes · Mismatched rules scramble the message even when the bits arrive safely.
  5. She reverses the same agreed rule · Decoding works because she applies the same rule in reverse.
  6. A letter in one file and a shade of grey in another · Text files read bits as letters, while picture files read them as colours.
  7. The cable is fine, the ends used different codes · Intact bits with a wrong reading point at a code mismatch, not a broken wire.
  8. Both sides know that 1, 4, and 3 count the letters in each word · The code works because both sides share the letter-count rule.
Worksheet · LightMySky