Anew horse owner estimated that the horse would eat 30 pounds of food a day. the horse was training for a race, so it actually ate 42 pounds per day. what is the percent error between the owner's estimate and the actual amount

Amount of food that the horse ate per day it trained for the race = 42 pounds
Amount of food the horse would eat was estimated wrongly by the owner = 30 pounds
These information's are already provided in the question. We can see that the owner of the horse had an error in calculating the amount of food the horse would eat per day. The percentage of error made by the owner of the horse needs to be found.
Total error made by the owner of the horse in calculating = (42 - 30) pounds
                                                                                           = 12 pounds
Then percentage error between
owner's estimate and the actual estimate = (12/30) * 100
                                                                   = 4 * 10 percent
                                                                   = 40 percent
Total percentage of error made was 40 percent.