Find the chosen number from the 100 square.

Here are eight clues to use:

  1. The number is greater than 9.
  2. The number is not a multiple of 10.
  3. The number is a multiple of 7.
  4. The number is odd.
  5. The number is not a multiple of 11.
  6. The number is less than 200.
  7. Its ones digit is larger than its tens digit.
  8. Its tens digit is odd.

What is the number?


Four of the clues are true but do nothing to help in finding the number. Four of the clues are necessary for finding it.

Can you sort out the four clues that help and the four clues that do not help in finding the number?

Click here to download the WHAT DO YOU NEED worksheet.

Click here for Notes for Teachers

This problem is adapted from the NRICH task of the same name with permission of the University of Cambridge. All rights reserved.

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One Response to What Do You Need?

  1. Ray Huntley says:

    I have used problems like this one with grade 4-6 in the UK. They enjoy seeing how the clues help them decide which numbers are still possible at each stage.
    After the learners have tried problems like this, they like to make up their own clues and test with each other.

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