Hannah's Sweets
How an almost routine Maths question grabbed the headlines
06 June 2015
Last month it was Cheryl and her birthday. Now it's Hannah and her sweets. What is it about these maths questions involving girls (or are they women, the puzzles don't say) that catapults them into the news headlines?
The question about Hannah and her sweets was part of the 2015 Edexcel Higher GCSE maths exam.
There are n sweets in a bag. Six of the sweets are orange. The rest of the sweets are yellow. Hannah takes a random sweet from the bag. She eats the sweet. Hannah then takes at random another sweet from the bag. She eats the sweet. The probability that Hannah eats two orange sweets is 1/3.
Show that n²-n-90=0.
It was a tricky question, but arguably not the hardest on the paper. But the fact that a probability question about sweets suddenly turned into a question about solving a quadratic equation seemed to make it the focal point of the Twitter frenzy about 'impossibly difficult exams' that took hold last week.
Various people tweeted to point out that questions like Hannah's Sweets have been asked many times before, and didn't make the headlines. So why now?
There are two reasons:
(1) Teenagers have got used to GCSE maths questions that gently take you through the steps that lead to a solution. Hannah's Sweets went back to the traditional 'O' Level style of requiring you to make all of those steps yourself, without any hints. In recent years the nearest exam to an O Level has been what's called the IGCSE, which many schools take in preference to GCSE. A couple of years ago, there was an almost identical question to Hannah's Sweets which caused no frenzy at all.
A bag contains x counters. 7 of the counters are blue. Sam takes at random a counter from the bag and does not replace it. Jill then takes a counter from the bag. The probability they both take a blue counter is 0.2
Form an equation involving x. Show that your equation can be expressed as x² – x – 210 = 0
But on closer examination, that IGCSE question has what I regard as a crucial difference. The IGCSE question prompts the student on what to do: 'Form an equation involving x. Show your equation can be expressed as...' . The entire hint about 'form an equation' was absent from the Hannah's Sweets question, yet the latter was pitched at a much wider audience than its IGCSE predecessor. The challenge to find n^2-n-90 appeared as if from nowhere, and I can see why many teenagers would have been freaked out by this.
(2) Today's news is increasingly driven by social media. People have always found maths exams hard, but in the past they didn't have the chance to broadcast their feelings to the world. Once #EdexcelMaths had begun to trend last Thursday, anybody who had taken the exam and not coasted through it would have been tempted to join in the fun. If you look through the threads, you'll see the same jokes repeated again and again (eg "Hannah has some sweets, solve n^2-n-90...wow, that escalated quickly"). And while thousands took to Twitter to express their apparent outrage, tens of thousands more didn't. Do we know that Twitter's view was representative? Or do empty vessels make the most sound?
The Hannah Sweets question is the type of problem designed to discriminate between the A* and the A grade students. It could, probably should, have been better worded. But despite that, maybe it worked.
Post script: A day after the fuss died down, I was sent a copy of a question from a 2002 Edexcel paper. Instead of Hannah and Sweets, it's about Heather and Beads. The structure of the question is practically IDENTICAL.
There are n beads in a bag. 6 beads are black and all the rest are white. Heather picks one bead at random from the bag and does not replace it. She picks a second bead at random from the bag. The probability that she will pick 2 white beads is 0.5.
Show that n²-25n+84=0
Which goes to show, if you do enough past papers, you probably won't get surprised by anything.