factor links (factorgrams)

an arrow means that a number divides exactly into another number ('is a factor of')

in this work it needs to be fairly often repeated that all the arrows that can be drawn have been drawn 

so you cannot have a number that divides into another without there being an arrow to show this

start off with students drawing the arrows themselves:

draw all the arrows that you can to show the relationship 'is a factor of'

note that for question (1) you cannot use e.g. 3 and 6 since there is no arrow between the two blank circles (i.e. one must not be a factor of the other)

for this reason, you should not use 1 or the number itself