Thank you guys.
Tried the pizza thing tonight, as coincidentally ds1 cooked pizza at school (although a bit nibbled)...the scenario would have fitted well in an episode of outnumbered:
Ds3 " I know, I know....we did this ages ago, when can we eat it.
Me. "Ok, now take three of the quarters and give me half of the 3/4 without cutting...or biting any pizza"
Ds3 " blank"
Me " can't do it...right put 3 x 1/4 bits back in the pizza shape now cut each quarter of the whole pizza in half.
Ds3 makes sure select bits have all sought after red pepper, cuts into 8
Me "now take 3/4 out of the tin"
Ds3 "we haven't got quarters anymore"
And on and on.....
I think the 3/4 x 1/2 may work, did not think of turning the scenario into a multiplication.
.. I will do that tomorrow morning...patience of a saint me!
Thankfully ds2 gets it after this morning's episode.