Answer: 9.70%
Step-by-step explanation:
The formula to find the percentage error is given by :-

Given : Actual mass of zinc oxide used by pharmacist = 28.35 g
Estimated mass of zinc oxide used by pharmacist =31.1 g
Now, 
i.e. 
i.e. 
Hence, the percentage of error on the basis of the desired quantity.= 9.70%
Example: Convert 0.125 to percent. Multiply 0.125 by 100: ...Example: Convert 0.35 to percent. Move the decimal point two places to the right: 0.35 → 3.5 → 35. ...Example: Convert 0.985 to percent. ...Example: Convert 1.2 to percent
1 deciliter equals 0.1 liter. So If a bottle contains 3.78 liters of water that’s 37.8 deciliter so there is more than 3.78 deciliter in a bottle of water
Check the picture below.
so, if we get the whole area of the figure, which will be the combined areas of those three rectangles, and if we get the area of the triangle, and then subtract that area from of the triangle from the whole figure's area, we're in effect making a whole in the total area, and what's leftover is the shaded area.
