Final answer:
To find the percentage of chocolate Lily has not eaten, subtract the amount she ate from the total mass of the chocolate and calculate the percentage.
Step-by-step explanation:
To find the percentage of chocolate Lily has not eaten, we need to subtract the amount she ate from the total mass of the chocolate and then calculate the percentage.
Step 1: Calculate the amount of chocolate Lily has not eaten by subtracting 30g from 220g: 220g - 30g = 190g.
Step 2: Calculate the percentage of chocolate Lily has not eaten by dividing the amount she has not eaten (190g) by the total mass of the chocolate (220g) and multiplying by 100: (190g / 220g) * 100 = 86.36%.