Hi Duncan, I have been trying to solve this equation and diagram for over a week now and am still at a loss. If at all possible can you help me? Here goes: P = 20 -2Q, how do I find the mid-point elasticity formulae to determine the price of elasticity demand when the rice changes from five to six dollars? I'm finding it difficult as to where the -2Q goes and where it goes on the diagram. Talk about confusing. I should have paid more attention at school with algebra but then who was to know that I wanted to get into business back then. Thanks A Hello again and thanks for the question. Depending on the level you are working at the answer if one of two possibilities You can apply the basic formula of Price Elasticity of Demand (PED) = % change in quantity/% change in price which in this case is ((7 – 7.5)/7.5 * 100)/((6-5)/5)*100) = 6.667%/20% = -0.3333 Or Mid Point PED = (change in quantity/mid quantity)/change in price/mid price) = (-0.5/7.25)/(1/5.5) = -0.37931 Different answers because the formulae are a little bit different. Two pages to help you: PED is an interactive spreadsheet file that I wrote for www.bized.ac.uk a couple of years ago … step by step help for you Mid point PED same site but I didn’t write this one. It’s a nice looking and very clear power point presentation and the bit you need is very, very clear: just keep pressing the page down key until you get to the sheets you need, not many! I hope this is helpful! DW