Answer:
To do this, you wold need to know the percent error formula.
Percent Error = (Actual value - Expected Value)/Expected Value x 100
Percent Error = (388 - 400)/400 x 100
P.E = (-12)/400 x 100
-0.03 x 100
-3%
(It could possibly positive, if they don't take negative)
Hope this helps!
