Answer:
12% decrease
Step-by-step explanation:
given:
In 2017, a chocolate bar had a mass of 250g.
In 2018, the mass of the chocolate bar was reduced to 220g.
The difference in mass is 250 - 220 = 30g
30 / 250 = 0.12 which is how much out of the 250g
0.12 x 100 = 12