To deduce the answer directly from the question, we can multiply throughout by 12,

* * * *
- - - + - = -
* 2 4 12

to give:

12 - 6* + 3* = 1*

12 - 3* = 1*

12 = 4*

3 = *

As required.

Puzzle 2

Starting in the bottom left corner and moving either up or right, one square at a time, adding up the numbers along the way, what is the largest sum which can be made once you have reached the top right corner?

We then repeat this for 100, 200, 300, up to 900 - which is 200 9's.

But from 900 to 999 we have an extra 100 9's as each starts with a 9.

So the total is 300.

Puzzle 5

Each empty white square in the grid contains one of the numbers 1, 2, 3,..., 8. Each of the horizontal and vertical equations must be true and each number must be used exactly once.