Choose any three by three square of dates on a calendar page.
Circle any number on the top row, put a line through the other
numbers that are in the same row and column as your circled number.
Repeat this for a number of your choice from the second row. You
should now have just one number left on the bottom row, circle it.
Find the total for the three numbers circled. Compare this total
with the number in the centre of the square. What do you find? Can
you explain why this happens?
Take any two digit number, for example 58. What do you have to do to reverse the order of the digits? Can you find a rule for reversing the order of digits for any two digit number?
Can you explain how this card trick works?
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
[This is an exercise for practice from the Hungarian KöMaL
magazine, September 2000 issue. You'll find many other challenging
problems in English on the KöMaL