SPACE ACADEMY · TRY, THINK, PLAY

Class 3: Number detectives

Translate representations, use place value and solve constrained number clues.

Play missionChapters

Try a quick challenge

Just a quick try. Not saved; no game rewards.

ExploreComparing quantities

Which is the greatest number: 285, 258, 825, 582?

  1. 825
  2. 582
  3. 285
  4. 258
Need a hint?

Compare the digits from the left. The first place that differs decides.

Answer & method
Answer A: 825

Comparing place by place from the left, the greatest number is 825.

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ReasonWorking backwards

A 3-digit number is less than 900 and is more than 800. Which of these can NOT be that number? 820, 182, 847, 868

  1. 847
  2. 868
  3. 182
  4. 820
Need a hint?

Three numbers fit every clue. Find the one that breaks a clue.

Answer & method
Answer C: 182

182 breaks a clue. The other three numbers fit them all.

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StretchWorking backwards

It is from 4496 to 4522. Its digits add to 18. Its ones digit is 9. Its tens digit is 0. What is the code?

  1. 4519
  2. 4590
  3. 4509
  4. 4510
Need a hint?

Keep a code only when every clue fits. One clue is not enough.

Answer & method
Answer C: 4509

4509 is inside the range, its digits add to 18 and its ones digit is 9.

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For grown-ups

Ideas to practise

  • Place value. A digit has a different value in each position. Count the places from the right.
  • Building numbers. Combine the place-value parts, including any zero places.
  • Comparing quantities. Compare the values, not the size or spacing of their pictures.
  • Number patterns. Look for the same change between neighbouring numbers.
  • Working backwards. Undo the last operation first, then undo the earlier operation.

A game mission has 8 untimed questions. Only the game saves choices and hints. A finished mission earns one launch charge and participation towards the Flight cabin in Star Navigator. The chapter goal is 8 different questions in finished sets; hints and wrong answers count as participation, not mastery. Some craft systems link more than one chapter.

Choose a level

Explore

Foundations: read a representation and practise the underlying idea.

  • Read a four-rod star abacus
  • Pick the base-ten blocks for a number
  • Read an arrow on a labelled number line
  • Build a number from place-value cards
  • Order numbers made from the same digits
  • Fill in a missing place-value number
  • Match numbers with their words
  • Round or step a number by tens and hundreds
  • Run a number through a rule machine
Play Explore

Reason

Paper-style reasoning: connect clues, interpret a diagram or work backwards.

  • Open a lock from three number clues
  • Build a number from place-value cards
  • Pick the number that fits every clue
  • Order numbers made from the same digits
  • Round or step a number by tens and hundreds
  • Solve number puzzles with odd, multiples and digits
  • Fill in a missing place-value number
  • Find the missing number in a chain of steps
  • Read a four-rod star abacus
Play Reason

Stretch

Higher-order practice: link conditions, test statements and avoid a tempting wrong method.

  • Pick the number that fits every clue
  • Solve number puzzles with odd, multiples and digits
  • Find two numbers from a total or a difference
  • Find the missing number in a chain of steps
  • Open a lock from three number clues
  • Run a number through a rule machine
  • Read an arrow on a labelled number line
  • Pick the base-ten blocks for a number
  • Round or step a number by tens and hundreds
  • Order numbers made from the same digits
Play Stretch

Levels change representations, clues and conditions, not just the numbers. These are practice formats, not validated exam-equivalent difficulty.

Using the feedback

Learning reports distinguish hinted answers from independent first choices. They consider up to 20 recent different, unhinted questions per skill and level, and wait for at least five before suggesting extra practice. Repeating the same question does not add evidence. Reports are practice evidence, not IQ scores, diagnoses, ranks or predictions of competition results.

Ask the learner to explain a drawing or check with objects too. Choose Explore or an earlier chapter when a step feels too large.

Sources & limits

The grade topics use SOF IMO Class 3 published topic syllabus as their primary reference. The SOF sample and CREST previous-year paper below informed representations and reasoning demands. Providers have different topic boundaries; their syllabi are not interchangeable.

Questions, diagrams, picture choices, hints and explanations are original Otterly work, not copied paper questions or publisher artwork. No Olympiad provider is affiliated with or endorses Space Academy. This is not complete exam preparation; follow classroom teaching and check the current official syllabus too. Independent educator review is still needed for difficulty and breadth.

Content and coverage notes. To report a confusing question, describe the grade, chapter, level and question on the contact page. Do not send children’s personal information.

Private, local saves

Game progress stays only in this browser, in three anonymous explorer slots. Clearing site data or closing a private session may remove it. Download a private backup from Help & saves; there is no cloud sync. The game checks saves before play and stops on save failures rather than pretending progress was saved.

These page examples never change a saved game. Game links carry question settings, not a learner’s answers. There are no names, school details, public profiles, chat, analytics or advertising SDKs in the game. Grown-up guidance · Privacy

Original Otterly practice, not an official exam. Game progress stays on this browser.