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. A two-bit code has 00=P, 10=Q and 11=R. Which unused pattern can represent S so every letter has its own pattern?

    • 00, already assigned to P
    • 01, not yet assigned here
    • 11, already assigned to R

  2. No code is given for the bits 01. What can you conclude about their intended message?

    • Their intended meaning has not been specified.
    • They must represent the letter B.
    • They must represent dark grey in every possible message.

  3. The same bit pattern can represent different things when different codes are used.

    Circle one:   True   False

  4. A sender uses 10=C and 00=A, sending 10 00 for CA. The bits arrive unchanged. A receiver's table has 10=D and 00=B. What does the receiver read?

    • DB
    • CA
    • BD

  5. Use 00=A, 01=B, 10=C and 11=D. What bits should you send for BD?

    • 11 01
    • 01 10
    • 01 11

  6. A message uses three bits per symbol. The bits arrive as 101001. Which grouping follows the rule without changing any bits?

    • 10 10 01
    • 101 001
    • 101 010

  7. A sends 10 intending the letter C. B receives the same unchanged bits but reads them as light grey using a shade code. Which explanation fits?

    • The bits changed during transmission.
    • The bits must mean C in all file types.
    • The bits were read with another code.

  8. Two friends send only the number of letters in each word. Both 'red kite' and 'big boat' become 3, 4. Why can knowing the rule fail to reveal which phrase was sent?

    • The digits must be read as letters.
    • Using an eight-bit byte for each digit restores the missing letters.
    • The phrases share word lengths.
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. 01, not yet assigned here · 00, 10 and 11 already represent letters. Assign the unused pattern 01 to S.
  2. Their intended meaning has not been specified. · Without the intended code, you cannot tell what 01 is meant to represent.
  3. True · A stated code determines the interpretation. The lesson's letter and shade codes give 01 different meanings.
  4. DB · The receiver reads 10 as D and 00 as B, producing DB because its table differs.
  5. 01 11 · B is 01 and D is 11. Keep their order: 01 11.
  6. 101 001 · Starting at the left, the first three bits are 101 and the next three are 001. The grouping is 101 001.
  7. The bits were read with another code. · The question states that the bits are unchanged. The output differs because the bits are interpreted differently.
  8. The phrases share word lengths. · The rule leaves out the letters themselves. Both phrases fit 3, 4, so the reading is not unique.
Worksheet · LightMySky