The price dropped by 0.08 dollars (subtract 3.20 and 3.12)
Divide this price drop over the original price
0.08/3.20 = 0.025 = 2.5%
The percent change is -2.5%
The negative is to indicate a price drop or decrease
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If you want, you can use the formula below
P = 100*(N - S)/S
where N = 3.12 is the new price and S = 3.20 is the start price, so
P = 100*(N-S)/S
P = 100*(3.12-3.20)/3.20
P = -2.5%
we get the same answer as before
