Addition and subtraction
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problemPair Sums
Five numbers added together in pairs produce: 0, 2, 4, 4, 6, 8, 9, 11, 13, 15 What are the five numbers?
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problemPairs
Ann thought of 5 numbers and told Bob all the sums that could be made by adding the numbers in pairs. The list of sums is 6, 7, 8, 8, 9, 9, 10,10, 11, 12. Help Bob to find out which numbers Ann was thinking of.
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problemCunning Card Trick
Delight your friends with this cunning trick! Can you explain how it works?
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problemPostage
The country Sixtania prints postage stamps with only three values 6 lucres, 10 lucres and 15 lucres (where the currency is in lucres).Which values cannot be made up with combinations of these postage stamps? Prove that all other values can be made up.
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problemPros and Cons
If p is a positive integer and q is a negative integer, which of these expressions is the greatest?
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