Start with a Venn Diagram. Ask them to draw it out and put the numbers where they think the numbers should go. Talk about overlapping: e.g. imagine two paper circles that overlap. The middle portion is thicker because two pieces of paper, i.e. double counted. Have to 'remove one layer of paper' - similarly the venn diagram has to add up correctly so take away a number so that you get the correct total:E.G.50 = total30 = road racers15 = fell racers12 = no racers50 = 12 + 30 + 15 - ?? = 7so 7 was double counted! --> 7 is the middle of the venn diagram --> 7 is the answer!12 + 30 + 8 = 50http://www.mathsgp.co.uk/wp-content/uploads/2017/07/badly_answered_2_foundation_1.pdf