Addition and subtraction

How is it possible to predict the card?

Different combinations of the weights available allow you to make different totals. Which totals can you make?

Just because a problem is impossible doesn't mean it's difficult...

Five numbers added together in pairs produce: 0, 2, 4, 4, 6, 8, 9, 11, 13, 15 What are the five numbers?

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.

Do you notice anything about the solutions when you add and/or subtract consecutive negative numbers?

In this game the winner is the first to complete a row of three. Are some squares easier to land on than others?

What is the sum of all the digits in all the integers from one to one million?

Use the differences to find the solution to this Sudoku.