PerspectivesMathematicsTheOptimalDartboardTo many people, darts is already a fiendishly difficult game, but now DavidPercy, Pr<strong>of</strong>essor <strong>of</strong> Mathematics at the <strong>University</strong> <strong>of</strong> <strong>Salford</strong>, has made it evenharder.He has created the ‘Optimal Dartboard’ by re-arranging the numbers in such away that they minimise the chances <strong>of</strong> a high-scoring random throw. As wellas alternating odd and even numbers, Percy’s board also groups the numbers insimilar scoring clusters.(1+2+1)/4 Dartboard Comparison13Normal dartboardRunning averages1211109OptimalNormalAverage80 5 10 15 20Position on dartboardOptimal dartboard40 | May 2013
“ People have been lookingat this problem for thelast 30 years, but only asa bit <strong>of</strong> fun,” Pr<strong>of</strong>essorPercy explains.“ But theywere using the wrongoptimality measureand also ignored the importance <strong>of</strong> havingalternating odd and even numbers. The idea isto make the dartboard as hard as possible.It is easier for a lucky throw to scorehighly in the left-hand side <strong>of</strong> the board,where there is a section containing12-9-14, with an average <strong>of</strong> 11.7, as wellas 16-7-19, with an average score <strong>of</strong> 14.“What they were looking at was tryingto make the difference between adjacentnumbers as large as possible, so that if youmiss a big number, you get a small number.But what you actually need to do is look atthe total score <strong>of</strong> two adjacent numbers andtry and make that as similar as possible all theway around the board.”Percy analysed the traditional board by tottingup the average scores for different sections<strong>of</strong> the board and laid out the plans for thenew board in a paper published in the journalMathematics Today.“The average <strong>of</strong> all the numbers on adartboard is 10.5, so put simply, you can gainby targeting those sections where the averageis higher than that,” he explains. He showedthat it was easier for a lucky throw to scorehighly in the left-hand side <strong>of</strong> the board,where there is a section containing 12-9-14,with an average <strong>of</strong> 11.7, as well as 16-7-19,with an average score <strong>of</strong> 14.With players traditionally trying to get from301 or 501 down to zero, the layout <strong>of</strong> theoptimal board also makes a big difference atthe end <strong>of</strong> the game, when players have to goout on a double. If they’re on an odd number,they’ll need to hit another odd number beforebeing able to go for a double. On the oldboard, even the worst player had a goodchance <strong>of</strong> hitting one close to the bottom <strong>of</strong>the board, with its cluster <strong>of</strong> four adjacentodd numbers 7, 19, 3 and 17.Percy’s new alternating arrangements hasput pay to this, along with another favourite,double 16. On the traditional board 16 and 8are next to each other, so if you miss double16 and hit single 16 instead, you then requiredouble 8, theoretically making it easier to hitas you already have your sights set on thatpart <strong>of</strong> the board. Similarly, the 10 and 6 areno longer adjacent, which makes finishingharder when players are on an even number.The dartboard was trialled at the BDO WorldPr<strong>of</strong>essional Darts Championships in Januaryby darts legend Bobby George, and severalprototypes have been developed by leadingdartboard manufacturer Winmau. However,there are no plans to replace the traditionalboard, the numbering <strong>of</strong> which is thought todate back to the 19th century.Modestly, Percy adds: “Maths is <strong>of</strong>ten aboutfinding the optimal solution to a problem andthis is the optimal solution to that particularproblem. I lay no further claims – it was justan interesting piece <strong>of</strong> work!”May 2013 | 41