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Substitution Cipher
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Substitution Cipher

11 to 14
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Find the frequency distribution for ordinary English, and use it to help you crack the code.

Weekly Challenges are here!
article

Weekly Challenges Are Here!

11 to 18
Weekly challenges are here for NRICH! To celebrate this event, we've collected a set of 20 essential problems for you to try.
Difficulties with Division
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Difficulties With Division

5 to 11
This article for teachers looks at how teachers can use problems from the NRICH site to help them teach division.
Bipin's Choice
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Bipin's Choice

7 to 11
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Bipin is in a game show and he has picked a red ball out of 10 balls. He wins a large sum of money, but can you use the information to decided what he should do next?
Peg Rotation
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Peg Rotation

7 to 11
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Can you work out what kind of rotation produced this pattern of pegs in our pegboard?
Today's date - 01/06/2009
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Today's Date - 01/06/2009

5 to 11
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What do you notice about the date 03.06.09? Or 08.01.09? This challenge invites you to investigate some interesting dates yourself.
Sort them out (2)
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Sort Them Out (2)

7 to 11
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Can you each work out the number on your card? What do you notice? How could you sort the cards?
Straight to Curves
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Straight to Curves

5 to 11
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How can you make a curve from straight strips of paper?
Worked Example: Counters in Bags
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Worked Example: Counters in Bags

16 to 18
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This worked example computes the number of ways we can move counters around in two bags to determine a probability of interest.
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