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Double Digit

Choose two digits and arrange them to make two double-digit numbers. Now add your double-digit numbers. Now add your single digit numbers. Divide your double-digit answer by your single-digit answer. Try lots of examples. What happens? Can you explain it?

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Not a Polite Question

When asked how old she was, the teacher replied: My age in years is not prime but odd and when reversed and added to my age you have a perfect square...

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Whole Numbers Only

Can you work out how many of each kind of pencil this student bought?

Sissa's Reward

Stage: 3 Challenge Level: Challenge Level:2 Challenge Level:2
According to an old Indian myth, Sissa ben Dahir was a courtier for a king. Sissa worked very hard and invented a game which was played on a board, similar to chess. The king decided to reward Sissa for his dedication and asked what he would like. Sissa thought carefully and then said, "I would like one grain of rice to be put on the first square of my board, two on the second square, four on the third square, eight on the fourth and so on." The king thought this was a silly request, but little did he know ...

Below is a chess board with the first few squares filled with grains of rice as Sissa asked for:

chessboard with 1 grain of rice in top left square, two grains in adjacent square, four grains in next square

How many grains of rice would there be on the 8th square?

How many grains would you need altogether in order to fill up to the 15th square?

Estimate how many grains you would need in total to fill the entire board in this way. Explain your thinking.
Perhaps Sissa was cleverer than the king thought!

The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice. More information on many of our other activities can be found here.
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NRICH is part of the family of activities in the Millennium Mathematics Project.