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Year 10 Computing — The trail you leave online

Work out how few harmless-looking facts it takes to narrow a crowd down to one person, and tell what a website is handed by you from what it is handed anyway.

Name: ________________________

  1. 1.In a group of 200 people, each year group is shared by 50 people; inside any one year group each birth month is shared by 5; and inside any one birth month each first initial is shared by 1. Match each set of facts to how many people could still be the person described.

    • Nothing at all is known
    • The year group
    • The birth month, without the year group
    • The year group and the birth month
    • The year group, the birth month and the first initial
    • 200
    • 1
    • 20
    • 50
    • 5

  2. 2.A form asks for 11 pieces of information about you. Four of them are genuinely needed to get a parcel to your door, and the rest are needed for nothing about the parcel at all. How many pieces is the form collecting that the parcel does not need?

  3. 3.A swimming pool has 1800 members. One in five of them swims before school, and one in three of those is in the same year group as you. How many members fit both of those facts?

  4. 4.A club has 720 members. Half of them are in the same year group as you. Of those, one in six has a birthday in the same month as you. Of those, one in twelve plays the flute. How many members share all three of those facts with you?

  5. 5.A game stores a nickname and a birth date for each of its 90 players. Another website stores a birth date and a real name for the same 90 people. Among the 90 there are 8 birth dates that are each shared by exactly two players, and every other birth date belongs to one player only. Laying the two lists side by side, how many of the 90 nicknames can be turned into a single real name?

  6. 6.In a group of 60 people, each year group is shared by 30 of them, each birth month by 5, each admission number by 1, each favourite sport by 12, each pairing of shoe size with birth month by 2, and each email address by 1. Sort each fact by how many people are left once you know it about somebody.

    Groups: Leaves exactly one person · Leaves more than one person

    • Their shoe size and birth month together
    • Their admission number
    • Their year group
    • Their favourite sport
    • Their email address
    • Their birth month

  7. 7.A club has 600 members. Put these facts in order of how many members each one leaves, fewest first.

    • Is in the same year group as you, which one member in every two is
    • Travels by bus, which one member in every five does
    • Plays the cello, which one member in every twenty-five does
    • Born in the same week as you, which one member in every hundred is

  8. 8.You visit a website and type nothing into it at all. Which of these does the website learn anyway?

    • a) Your date of birth
    • b) The time you arrived
    • c) The password to your email
    • d) The name of your school

Answer key — Year 10 Computing — The trail you leave online

  1. 1. Nothing at all is known → 200; The year group → 50; The birth month, without the year group → 20; The year group and the birth month → 5; The year group, the birth month and the first initial → 1
  2. 2. 7
  3. 3. 120
  4. 4. 5
  5. 5. 74
  6. 6. Their year group → Leaves more than one person; Their birth month → Leaves more than one person; Their admission number → Leaves exactly one person; Their favourite sport → Leaves more than one person; Their shoe size and birth month together → Leaves more than one person; Their email address → Leaves exactly one person
  7. 7. 1. Born in the same week as you, which one member in every hundred is 2. Plays the cello, which one member in every twenty-five does 3. Travels by bus, which one member in every five does 4. Is in the same year group as you, which one member in every two is
  8. 8. b) The time you arrived