Addition and subtraction

problem
Adding all nine

Age

11 to 14

Challenge level

Make a set of numbers that use all the digits from 1 to 9, once and once only. Add them up. The result is divisible by 9. Add each of the digits in the new number. What is their sum? Now try some other possibilities for yourself!
problem
Have you got it?

Age

11 to 14

Challenge level

Can you explain the strategy for winning this game with any target?
problem
Cinema problem

Age

11 to 14

Challenge level

A cinema has 100 seats. How can ticket sales make £100 for these different combinations of ticket prices?
problem
Consecutive seven

Age

11 to 14

Challenge level

Can you arrange these numbers into 7 subsets, each of three numbers, so that when the numbers in each are added together, they make seven consecutive numbers?
problem
Multiply the addition square

Age

11 to 14

Challenge level

If you take a three by three square on a 1-10 addition square and multiply the diagonally opposite numbers together, what is the difference between these products. Why?
problem
Calculation 2000

Age

11 to 14

Challenge level

Weekly Problem 49 - 2013
What is the value of 2000 + 1999 × 2000?
problem
Debasing the coinage

Age

11 to 14

Challenge level

How much lighter will £5 worth of 5p's be with these new lighter coins?
problem
Crossed ends

Age

11 to 14

Challenge level

Crosses can be drawn on number grids of various sizes. What do you notice when you add opposite ends?
problem
Can you make 100?

Age

11 to 14

Challenge level

How many ways can you find to put in operation signs (+, −, ×, ÷) to make 100?
problem
Number pyramids

Age

11 to 14

Challenge level

Try entering different sets of numbers in the number pyramids. How does the total at the top change?