(HSC Maths Extension 1 ) Jacqui from Dux College runs through the common ‘birthday problem’, which asks you to show that “In a group of 23 randomly chosen people, the probability that at least 2 people share the same birthday is greater than 50%”. If you try to plug your numbers directly into your calculator, you’ll find the numbers are too big. You first need to cancel out some terms before using your calculator!