We have to calculate the percent decrease in temperature and to choose the correct answer. We can solve the proportion: 320 / 280 = 100 / x; then we will cross multiply. 320 x = 280 * 100; 320 x = 28,000; x = 28,000 : 320 ; x = 87.5 %. Finally : 100% - 87.5 % = 12.5 %. Answer: The percent decrease is C. 12.5 %.
