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Pebbles

Place four pebbles on the sand in the form of a square. Keep adding as few pebbles as necessary to double the area. How many extra pebbles are added each time?

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Adding All Nine

Make a set of numbers that use all the digits from 1 to 9, once and once only. Add them up. The result is divisible by 9. Add each of the digits in the new number. What is their sum? Now try some other possibilities for yourself!

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GOT IT Now

For this challenge, you'll need to play Got It! Can you explain the strategy for winning this game with any target?

Factors and Multiples Puzzle

Stage: 3 Challenge Level: Challenge Level:1

To try this puzzle you will need a copy of the playing board and cards. You can download a copy to print.

board
  1. Cut out the $10$ heading cards and put one in each of the $10$ spaces round the playing board.

    heading cards

  2. Cut out the $25$ number cards and place each one in a different square on the playing board so that the number satisfies the condition given by the heading card for that row and the condition given by the heading card for that column.

    number cards

    By rearranging the heading cards and the number cards, try to fill as many squares on the playing board as possible.
Can you fill all the squares on the board at once?

You can discuss a follow-up question related to this problem on the NRICH Projects site.