Here is a grid of four "boxes":
You must choose four different digits from $1 - 9$ and put one in each box. For example:
This gives four two-digit numbers:
|$52$||(reading along the $1$st row)|
|$19$||(reading along the $2$nd row)|
|$51$||(reading down the left hand column)|
|$29$||(reading down the right hand column)|
In this case their sum is $151$.
Try a few examples of your own.
Is there a quick way to tell if the total is going to be even or odd?
Your challenge is to find four different digits that give four two-digit numbers which add to a total of $100$.
How many ways can you find of doing it?
You may be interested in the other problems in our Mastering Mathematics: Developing Generalising and Proof Feature.
This problem is adapted from Make 200 from 'Mathematical Challenges for Able Pupils Key Stages 1 and 2', published by DfES.