How do you calculate percentage error in math?

In math. Here's the question:



a) Calculate (3x2.1)^3 / 7x1.2 --%26gt; equals 29.7675



b) Write the answer to part a) correct to 2 significant figures --%26gt; 30



c) Calculate the percentage error when the answer to part a) is written correct to 2 significant figures.



???How do you calculate percentage error in math?
http://orgchem.colorado.edu/hndbksupport鈥?/a>

That equation is from my chemistry class, but I'm pretty sure it'll work for this problem, too.



30 / 29.7675 * 100 = 100.78%