## Principles of Microeconomics, 7th Edition

The midpoint method is calculated as $[(Q2-Q1)/[Q2+Q1)/2]]/[(P2-P1)/[(P2+P1)/2]]$ Plugging in the numbers, we get: $[(110-90)/[(110+90)/2]]/[(12-8)/[(12+8)/2]] = 20/100 / 4/10 = 1/2$