This is a simple little investigation which can prove to be quite tricky. On a 3 by 3 grid how many counters can be placed without getting three in a row? You can have a single counter in a row or two, but not three. Are there different arrangements of the possible maximum number? Once the three by three grid has been cracked why not try the same task with a 4 by 4 grid? Good for logical thinking and working in a methodical way, but I would definitely suggest that you get the counters out to solve this one. Go to 'Not three in a row'.