Need help with Math (on case in Consulting Bible)

Hey All - I've recently started doing cases out of WSO's Consulting Bible. If anyone has this, I'm having trouble with the math on Case 5 (Tommy's Tennis).

They want us to calculate what the new price should be given that there are 15 courts currently costing $20 an hour but there are 20 people that want to use the courts (ie excess demand of 5). We know that price elasticity is -1 (If the price of courts goes up by 10%, the number of people wanting to play will go down by 10%).

The formula they use to calculate what the new price should be is: New Price = [(% Change in Vol. / Elasticity) + 1] * Old Price New Price = [(-25% / -1) + 1]*$20 New Price = $20

Does anyone understand the math going on here? I think the -25% comes from 5/20 but I'm not sure why this formula works or what the intuition is. Any help would be much appreciated!

4 Comments
 

Is that right? I'm assuming the formula you have is "New Price = [(-25% / -1) + 1]$20 " or (1.25)20 which equals $25

 

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