Horace speedometer reads 60 miles per hour, but during a road test he finds that he was actually driving 58 mph. what is the percent error in Horace's speedometer?

Question

Horace speedometer reads 60 miles per hour, but during a road test he finds that he was actually driving 58 mph. what is the percent error in Horace's speedometer?

Answer 1

speedometer reads 60 mph

actual speed is 58 mph

percent error =?

absolute error 60-58 = 2 mph

2/58 = 1/29 = 0.03448275862068965517241379310.... (those 28 digits repeat endlessly. any calculator will round it off at about 2,3 or more digits but far less than 28)

= about 3.45% error

or

= about 3.4%

or

= about 3% rounded to nearest integer

a mistake would be to round 3.45 to 3.5, then round 3.5 to 4%. 3% is correct for rounding to 1 digit percentage

another mistake would be to calculate 2/60 as the relative error = 1/30 = 3 1/3% = 3.333...% but you'd still get 3% that way when rounding to 1 digit.