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Jack does a 20-question quiz. How many questions didn't he attempt?

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Weekly Problem 52 - 2009

How did Jenny figure out that Tom's cards added to an even number?

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The sum of each column and row in this grid give the totals as shown. What number goes in the starred square?

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From only the page numbers on one sheet of newspaper, can you work out how many sheets there are altogether?

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Can you find numbers between 100 and 999 that have a middle digit equal to the sum of the other two digits?

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Repeat a pattern of numbers to form a larger number. Can you find the sum of all the digits?

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What is the largest number of digits that could be erased from this 1000-digit number, to get a surprising result?

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Alberta won't reveal her age. Can you work it out from these clues?

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Can you find a number and its double using the digits $1$ to $9$ only once each?