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

Weekly Problem 52 - 2009

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

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

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

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

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

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

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

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