To calculate the percent of error, we use the formula [tex] (|\frac{Actual value-Estimated value}{Actual value}|)*100[/tex].
If we plug in the numbers from this problem, it looks like this:
[tex](| \frac{67-78}{67}|)*100[/tex]
[tex](| \frac{-11}{67}|)*100[/tex]
[tex](\frac{11}{67})*100[/tex]
[tex].1642*100[/tex]
16.42% is the percent error of Andy's estimation.