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Magic Bag
A magic bag contains some black balls and some white balls. Two balls are removed simultaneously and they are both the same colour. The magic bag says ‘the probability of this happening is 0.5’. The number of black balls originally contained in the bag is given and the challenge is to work out how many white balls there were.
The different problems presented all link to triangular numbers and there then follows an invitation to prove that the result will always hold. An alternative method of working is given which avoids triangular numbers and brings in work on quadratic equations.
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Magic Bag: presentation 436.56 KB
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Magic Bag: printable resource 2.68 MB
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Magic Bag: presentation 436.56 KB -
Magic Bag: printable resource 2.68 MB
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