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Computing and logic shelf · Learning guide · Class 5

Detective Dhruv and the Secret Rules

AND is two switches in one line: the bulb lights only if both are closed. OR is two switches side by side: either one lights the bulb. NOT flips true to false and false to trueAND: both switches in one lineone switch open → no lightOR: switches side by sideeither one closed → light!NOT flips ittruefalsefalsetrue
AND is two switches in one line: the bulb lights only if both are closed. OR is two switches side by side: either one lights the bulb. NOT flips true to false and false to true

"Step forward if you are wearing white shoes AND you have a water bottle." Dhruv has white shoes but no bottle. Should he step forward?

What you will learn: the three secret rules AND, OR and NOT, how a detective uses them to solve a mystery, and how to spot a bad argument.

Small test at the end: scroll down to the end of this page for five short questions that check what you have learnt. Tap an answer, then press Check answer. Go to the questions ↓

Jump to: The story · Now try it · Check yourself · For grown-ups · For teachers

Safety first

Step forward carefully. No running.

Keep it safe:

  • Leave enough clear space for every player, including anyone who uses a wheelchair or a walking aid.

The secret rules game

Dhruv is in Class 6. Everybody calls him Detective Dhruv, because he never says "I think" without saying "because" too.

On Monday in PT, Coach Rao invented a new game.

"Step forward if you are wearing white shoes AND you have a water bottle."

Dhruv had white shoes but had left his bottle in class. He stayed where he was. Only three children stepped forward.

"Now step forward if you are wearing white shoes OR you have a water bottle."

This time Dhruv stepped forward, and so did nearly everyone. Ayaan, who uses a wheelchair, rolled forward with them: he had his bottle in his lap.

"Last one. Step forward if you are NOT wearing a cap."

Everyone in a cap stayed back, and everyone else stepped forward.

Dhruv's friend Tara (yes, the same Tara from Dadi's chai stall) whispered, "Three tiny words, and the whole line changes!"

The secret rules:

  • AND: both parts must be true.
  • OR: at least one part must be true (one, the other, or both).
  • NOT: flips the answer: true becomes false, and false becomes true.

1. The case of the missing cricket bat

At the end of lunch break, the Class 6 cricket bat was missing from the sports room.

Dhruv took out his notebook and collected clues, not guesses:

  1. The sports room is locked. So the person had a key AND was at school at lunch time.
  2. The watchman saw someone go in, and they were NOT wearing a red house T-shirt.
  3. The bat cover had fresh mud on it, from the cricket ground OR the school garden.

Then he made a table of the four children who might have been there.

A clue table of four classmates showing who has a key, who was at school at lunch, shirt colour and where mud came fromNameKey?At school at lunch?ShirtMud fromHarpreet✔✔red?Kabir✔✔bluegardenMeena✘✔green?Arjun✔✘ (home)blue?Clue: has a key AND was at school AND NOT in a red shirt
A clue table of four classmates showing who has a key, who was at school at lunch, shirt colour and where mud came from

Dhruv went through it, one rule at a time.

  • Meena has no key. The AND rule fails, so it wasn't Meena.
  • Arjun has a key but went home for lunch. The AND rule fails again.
  • Harpreet has a key and was at school, but he was in a red shirt. The NOT rule rules him out.
  • Kabir has a key, was at school, wore blue, and had mud from the garden. Every clue fits.

2. The detective checks before blaming

The class started whispering: "Kabir stole the bat!"

But Dhruv held up his hand. "Clues tell us who to ask, not who to blame." So he went and asked Kabir.

Kabir laughed. "Coach Rao gave me the key. The bat handle was loose, so I took it to the garden tap to clean it, then to the art room to glue the grip. It's drying on the windowsill!"

And it was. Nobody had stolen anything.

The rule: clues help you find the best explanation, but a good detective checks it before deciding.

3. Bad arguments Dhruv refused to believe

While the bat was still missing, two classmates were sure they knew the answer.

  • "It must be Arjun, because Arjun is always naughty."
    • Dhruv: "That's an attack on Arjun, not a clue about the bat. And he wasn't even at school."
  • "Everybody says it was Meena, so it must be Meena."
    • Dhruv: "If everybody says it, I still need a reason. Many people can be wrong together."
Detective Dhruv with a magnifying glass, saying show me the clue, not the name-calling“Show me the clue,not the name-calling.”— Detective DhruvClass 6
Detective Dhruv with a magnifying glass, saying: Show me the clue, not the name-calling

The rule: a good argument gives evidence about the thing itself, not insults about a person or "everyone says so".

4. Your turn: use the secret rules

  1. School rule: "You may use the computer lab if you have finished your homework AND a teacher is present." A teacher is present, but Tanmay hasn't finished his homework. Can he go in?
  2. Mela notice: "Free entry if you are under 10 OR over 60." Dadi is 65. Tara is exactly 10. Who gets in free?
  3. Corridor sign: "Do NOT run." Is walking allowed? Is hopping allowed?
  4. A new clue arrives in the bat case: "The person was NOT at school at lunch." Using the table, who fits now? Does that match the other clues?
Check your answers
  1. No. AND needs both parts, and the homework part is false.
  2. Dadi gets in free (over 60). Tara doesn't: she is exactly 10, and "under 10" means 9 or younger. Small words matter!
  3. Walking is allowed: the sign only forbids running. Hopping is a puzzle, because the sign doesn't mention it. Real rules often need a sensible grown-up to decide what they meant.
  4. Only Arjun fits that one clue, but it clashes with clue 1, which says the person was at school. When clues contradict each other, a detective checks which clue is wrong instead of picking a favourite.

Fun fact: your phone is made of secret rules

Every modern computer and smartphone contains billions of tiny switches called transistors, wired into "gates" that do exactly AND, OR and NOT, over and over, billions of times a second. Everything on a screen, from games to videos, is built from these three little rules.

Where the story stops being true

  • Real detectives use many kinds of evidence, and clues can be wrong: a watchman might remember a shirt colour wrongly.
  • In everyday talk, "or" sometimes means only one: "Tea or coffee?" usually means pick one. In logic, OR also allows both.
  • Computer switches aren't really little doors. They are tiny electrical parts, but they follow the same rules.

🧠 Logic corner

This guide is the Logic subject, and you used four thinking tools:

  • AND, OR, NOT: joining and flipping conditions.
  • Ruling out (deduction): removing anyone who breaks a rule until one possibility is left.
  • Best explanation: Kabir fitted every clue, but you still checked.
  • Spotting bad arguments: insults and "everyone says so" are not evidence.

You'll meet these tools again in the maths, science and language guides, in their own Logic corners.

Start here (Class 4)

Play with one rule at a time, using things everyone can see: "Stand up if you are wearing something blue." Then try one AND rule and one OR rule. Say who you think will stand up before anyone moves.

Go further (Classes 6–7)

Make a truth table for AND and for OR: two columns for the two parts (true or false), and one for the answer. There are four rows, because there are four ways to fill the first two columns. Then find a rule that is always true, such as "you are wearing white shoes OR you are NOT wearing white shoes", and explain why.

Words to know

Condition
a statement that is either true or false for each person, such as "wearing a cap".
AND
both parts must be true.
OR
at least one part must be true (one, the other, or both).
NOT
flips the answer: true becomes false, and false becomes true.
Evidence
a fact that helps show whether something is true.
Deduction
using rules and facts to reach a conclusion that must follow from them.
Transistor
a tiny electrical switch inside a computer chip.

🧪 Now try it

The Secret Rules Game

  • about 25 minutes

You need: 4 or more players (family or classmates), paper slips, a pencil

You make: six rule cards, a prediction tally, and one rule of your own that fooled someone

Three rule cards, AND, OR and NOT, and a tally of how many players were predicted to step forward and how many really didRule cards: who steps forward?ANDwearing blue ANDhas a watchORwearing blue ORhas a watchNOTNOTwearing a capTally: predicted / stepped forwardAND: 2 / 2 OR: 4 / 5NOT: 3 / 3
Three rule cards, AND, OR and NOT, and a tally of how many players were predicted to step forward and how many really did

The safety notes for this activity are at the top of the page.

  1. Notice

    Look at the players. List three things that are true or false for each person (for example: wearing something blue, has a watch, has had lunch).

    Grown-up: "Which facts are clear yes-or-no, and which ones could people argue about?"

    Teacher aim: Choosing conditions that are clearly true or false, the building blocks of logic.

  2. Guess

    Write six rule cards: two with AND, two with OR, and two with NOT. For each card, predict who will step forward.

    Grown-up: "Before we play, who do you think steps forward for the OR card, and why?"

    Teacher aim: Predicting outcomes by applying AND, OR and NOT.

  3. Try

    Read each card aloud. Everyone steps forward only if the rule is true for them.

    Grown-up: Make sure everyone steps carefully and nobody runs. A player who can't step can raise a hand instead.

    Teacher aim: Testing predictions in a physical, whole-body way.

  4. Observe

    Tally each card: predicted vs actually stepped. Which kind of rule (AND, OR or NOT) did you predict best? Which caught people out?

    Grown-up: "Did anyone step forward by mistake? Was it the rule or the way it was read?"

    Teacher aim: Recording results and finding where reasoning slipped.

  5. Explain

    Explain the difference between AND and OR to someone, using one of your cards. Then explain why "tea or coffee?" at home is different from OR in logic.

    Grown-up: "Show me with one card how NOT flips the answer."

    Teacher aim: Explaining logical connectives, and the gap between everyday "or" and logical OR.

  6. Ask another question

    Make a double rule, like "wearing blue AND NOT wearing a watch". Can you write one that nobody fits? One that everybody fits?

    Grown-up: "Where in real life do we see rules like these, such as forms, offers and signs?"

    Teacher aim: Combining connectives; leads towards truth tables and the logic gates inside computers (Classes 8–10).

Done when: you have six rule cards, a tally of predictions, and one double rule you invented.

Make it on paper. Keep it with you. Nothing to upload.

Check yourself

Five questions about what this page teaches. Choose an answer and press Check answer, or open "See the answer and why". Nothing is saved or sent: your choices stay on this screen and disappear when you leave or reload the page.

  1. Question 1 of 5"Step forward if you wear glasses AND have a bag." Lalremruati wears glasses but has no bag. What should she do?

    See the answer and why
    • A. Step forward, because she has one of the two Not this one. That would be the rule for OR. With AND, one out of two isn't enough.
    • B. Stay where she is: AND needs both parts Correct. Glasses is true, but bag is false, so the whole condition is false.
    • C. Step halfway forward Not this one. Secret rules give a clear yes or no. There's no "half true" here.
    • D. Wait and see how many others step forward, then do what most of them do Not this one. The rule is about Lalremruati's glasses and bag, not about what anyone else does.
  2. Question 2 of 5"A prize for anyone who scores a goal OR saves a penalty." Sam does both. What happens?

    See the answer and why
    • A. Sam gets the prize: OR is true when both are Correct. Both parts are true, so the condition is true.
    • B. Two prizes, one for each Not this one. The rule says a prize. Doing both makes the condition true, but it doesn't double the prize.
    • C. No prize, because you're only allowed to do one of the two things Not this one. That's the everyday "either-or" meaning, as in "tea or coffee?". In logic, OR includes both.
    • D. Sam must choose which one counts Not this one. The rule doesn't ask anyone to choose. Either one alone would be enough.
  3. Question 3 of 5Which is the best reason to think someone took the bat?

    See the answer and why
    • A. "He is always naughty." Not this one. That's about the person, not the bat. Even naughty people are often innocent.
    • B. "Everyone in class thinks so." Not this one. Lots of people believing something doesn't make it true. A crowd can be wrong together.
    • C. "The watchman saw him carry the bat out at lunch." Correct. That's evidence about the bat itself, at the right time and place. It's still worth checking, but it's a real clue.
    • D. "He was the last one to leave the class yesterday, after everyone else." Not this one. The bat went missing today at lunch, so yesterday's timing doesn't connect to it.
  4. Question 4 of 5A zoo sign says: "Do NOT feed the animals." Which of these is allowed?

    See the answer and why
    • A. Feeding them just one small biscuit Not this one. One biscuit is still feeding. NOT means none at all.
    • B. Throwing food near them, not to them Not this one. If the animals can eat it, that's still feeding, just from further away.
    • C. Feeding them when no guard is looking Not this one. The rule doesn't change when nobody is watching.
    • D. Taking photos of the animals Correct. The sign forbids only feeding. Taking photos isn't feeding.
  5. Question 5 of 5"You may enter the library if you have an ID card OR a teacher's note." Joseph has no ID card and no note. Can he enter?

    See the answer and why
    • A. No: both parts are false, so the OR is false Correct. No card and no note means the whole condition is false.
    • B. Yes, if he asks nicely Not this one. The rule doesn't mention asking. Only the card or the note counts.
    • C. He can go halfway in Not this one. Secret rules give a clear yes or no.
    • D. Yes, because OR rules are easy to pass and let most people through Not this one. OR needs at least one part to be true. Here both parts are false.

Same spark, other subjects

Rules and who decides

Rules a computer follows, rules people argue about, and who gets to decide.

For grown-upsThe safety notes are at the top of the page.

  • Play the "secret rules" game at home: "Clap if you had rice AND dal today" or "Clap if you have a sister OR a brother".
  • When your child accuses someone ("He did it!"), ask, like Dhruv: "What's the clue?".
  • Point out "or" in daily life and ask, "Does this one mean one, or both?"

For teachersLearning aims, links and what to look for.

  • Connects to: following instructions and conditions, classifying, reading tables, and the reasoning sections of maths and mental ability practice (Classes 4–7). It also prepares for Boolean logic and flowcharts in later computer science classes. There is no single textbook chapter for this.
  • Look for three things:
    • The child applies AND, OR and NOT correctly to a new rule.
    • The child rules out options using a table.
    • The child can say why "everyone says so" or an insult isn't evidence.
  • Class variation: run the PT game, then let pupils write their own AND / OR / NOT rules. Classmates predict who will step forward before testing.

These links are general. They have not been checked against a specific board syllabus.

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