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?

This problem is adapted from Make 200 from 'Mathematical Challenges for Able Pupils Key Stages 1 and 2', published by DfES.