It involves a selection of boxes which are linked together. Each box is divided into two sections - there is a number on top and a space underneath.
There's only two rules: every number on top of a box equals the total of the answers in the bottom of the box linked to it and no number may be used more than once. (A list of numbers you may use will be provided).
Confused? Don't panic. Let me guide you through an example.
You need to put 1, 2, and 3 into the three boxes. The box with 4 in it is linked to the boxes with the 3 on top and the 5 on top. Therefore, the numbers you put into the '3' and '5' box must add up to 4. In the same way '3' + '4' = 5 and '4' + '5' = 3.
I suggest fitting a smoke detector to your head to attempt these.
BRAIN TEMPERATURE: NORMAL
BRAIN TEMPERATURE: HOT
BRAIN TEMPERATURE: SIZZLING
BRAIN TEMPERATURE: CRITICAL
BRAIN TEMPERATURE: TOO HOT FOR WORDS
You are now approaching one of the most lethal puzzles on the planet. It is so hard that it is on the edge of meltdown and some of the numbers have evaporated into * symbols. It is still possible to fill in the answers, but if you are of a nervous disposition DO NOT ATTEMPT THIS PUZZLE.
BRAIN TEMPERATURE: EXPLODED